TS

Care to explain why you feel platonic vibes?

Was he too reserved? Or talk too much? Or talk boring things?

Or the way he treats you at the date?

Or maybe its his physical appearance?

How did he bring up this statement? Did you ask or did he "announce" it on his own?

Depending on the context, his intention may come off differently...
A) he announced to imply he's "in demand".
B) you asked so he simply just answered
C) the conversation just flowed naturally, he thought he'd tell you as an honest person
Well, you already crossed him off your list, so he's just agreeing to stay friends. Rejection from a side easily turns mutual because it's a total turnoff to a neutral impression.
"Serious" to me was reflection of how he treated the relationship, I don't think that was a bad thing. I guess you were thrown off by the 180° vibe change -- I don't think he meant to deceive or anything malicious... Tbh it really just sounded like maybe he wanted to show a prim and proper self or he was just really socially awkward.

I don't think any precaution is needed because like was nihility said, you can do all your prep work to anticipate, and the reality will still surprise you every time, for better or worse. I do think maybe you can shift your mindset a little: be more open/accepting to one's awkwardness, as long as the honest intentions are there. Give people time to get over their own awkwardness.

2 possibilities:

1. He finally met you in person and didnt like what he sees

2. He screwed up on the first date. Pretty common also. Could be nervousness, inexperience.

If u think its the second, isnt it too hasty to give up on just one date?

From your explanation, it seems that you're the one who brought up the "just be friends" topic first? There's a possibility he took that as a sign of rejection and just agreed since he can't force you to like him.

Still, if you want to give this a chance, just be direct and ask him about the situation instead of double guessing each other. I'm sure he'll appreciate it. There's nothing to lose, right?

Welp, case closed I guess lol! Best not to bring up the friendship topic the next time because that's like a very common rejection excuse and can be easily misinterpreted.

I don't think there's any foolproof way to know since everyone is different.

It's fair to drop someone if you're not feeling the vibe, but I feel a single date is a bit too early to tell, unless there's something that really turned you off? Some people may need more time to warm up before comfortable in showing their true self (the good or bad). Who knows!

Relationship cultivation/building — I'm afraid there's no shortcut.

It’s just like learning you need to allocate time to study and grow. The same applies to relationships. A strong and genuine relationship cannot be built without the investment of time. Through that time, we experience both the good and the bad in the other person. We begin to appreciate their strengths, admire their values, and gradually learn to accept their flaws and weaknesses.

Without the passage of time, none of this deeper understanding can occur. If you believe there’s a shortcut or faster way — humanity has been trying for thousands of years, and yet the truth remains: there is no substitute for time.

If you're still in doubt, consider this simple observation:
Would you be more willing to follow a leader within your organization who has groomed you, instilled values in you, and fought for your growth over the years —
or someone hired externally, who issues instructions without knowing your personal strengths, weaknesses, or working style? In my experience, 10 out of 10 people would prefer to follow the one who invested in them — not the latter.

This analogy holds true for male-female relationships as well: just as it takes time for trust and rapport to develop between leader and subordinate, it takes time for a relationship to mature. With this in mind, "time" is not an optional ingredient. Like it or not, you must spend it.

Now, if you already know you can’t save time — only use it — then why worry about someone “wasting” your time? Do you have a better alternative? No, you don’t.

You're left with three options:

Option A: You worry about wasting time and do nothing — but time will pass anyway.

Option B: You try, spend time, but don’t find the right person — and time still passes.

Option C: You try, spend time, and eventually find the right one — and yes, time passes just the same.

Among these three, none can stop time from passing.
But if you try, at least there's a chance you’ll end up with Option C.
If you do nothing but worry, your chances of success drop to zero.

So don’t overthink. Focus only on what’s within your control and give it your best. The outcome, if beyond your control, is fate.
And if Heaven wants us to walk a certain path, who are we to defy Heaven’s instruction?

Message him back and apologise for jumping the gun, explain that you confided in someone who pointed out the possibility that he was shy/nervous/awkward, hence the change in vibes. (And ask if he really was?)

Fat chance you ain't getting anything back and worst case, you get ghosted/blocked. But, I think there's a slim chance, just maybe, that he was slightly interested so might agree to a 2nd round and maybe with this honest exchange, something may feel different. Hear each other out about your feelings without judgement, maybe with this honest exchange you might learn something new. If you want to increase your chance then treat him on 2nd round lo.

Caveat: only do this if your gut feeling determined he's a sane/normal guy. Someone crazy might take revenge/humiliate you.

Why do this? Well, mainly is to humour me lol kind of an experiment to see how things will go. Personally I did things way out of character and learned from the outcomes and also my own feelings what I dis/like, and there I was able to change for the better (or at least what it means to be me version that I'd like).

If a guy wants to keep seeing you he is interested.
If undecided after first date, can ask for second one.

I used to be the one wanting to date for 10x before making it official until I meet a girl where we dated like 4x then I ask her to be official.

Normally how do you feel after the first date, then what's his action after the first date, did he follow up with you?, if both of you enjoyed each other you would like to see each other again.
My case is different, not every guy like me. Normally guys 2-3 dates can find out for themselves.
My previous case on 3rd date, i confessed, then kena rejected 

When you are official just stop swiping. Continue swiping can be tiring.

I am a very weird person. I go by checklist. I don't go by looks or chemistry. If the girl have what I want on my checklist then I will continue seeing her. I call it my non negotiables. You must have a set of non negotiable. Cannot have too many. I limit it to 6 only.

I date to marry. Not date for fun. So I need to see if she got what it takes to be a good wifey and good mother. Always ask yourself what to you date for? Fun, companionship, sex, marriage? Keep in mind some guys not serious. They like the feel of the chase.

You can always search but, yes there will always be better one but need to ask yourself is the one in front good enough or you want more. I had my answer already. She is good enough. Most important for me is she is frugal. That's my most important criteria.
Looking like the person is one thing. I check their background to see if they are telling the truth about their job.

Same here. I never put any hopes into the first date/meeting. I always expected to be rejected. Make my life easier.

I'll give a radical suggestion, it'll be way out of your comfort zone but maybe that may spur a change

Message him back and apologise for jumping the gun, explain that you confided in someone who pointed out the possibility that he was shy/nervous/awkward, hence the change in vibes. (And ask if he really was?)