From the price viewpoint, let say EURUSD, the price in EURUSD for demo account has a little different than the EURUSD in real account, especially in news release time, because the servers lag time are different. But this is not big problem. If the method is working well, slightly a few pips different won't degrade the significant performance after long term average.
In fact, the endowment effect (one of the psychology element) of trader are different form demo account and real account players. If they trade in demo, they did not own or loss something in real, so the heart will no pain or suffer so much. Most of the time, they trade with calm mind.
However, if they trade in real account and loss money, their pain is 2x than the amount of loss. This means if u loss USD 100, ur heart pain is equivalent to u loss in USD200. In this case, trader probably wish to do something more risky next time in order to gain back the loss money. They are much willing to risk next time. Or probably suicide /depressed (because too much pain in heart) after loss very large of amount.
In another situation, if he win money in real account, he probably get the happiness that is 1x the amount of win. This means u win USD100 is same level of happiness that u win USD100 (not USD200). In return in action, trader probably is trying to avoid risk and close the trade which has little profit (but have not hit TP). At the end, trader is not do what he planned earlier.
That is why u probably find ppl say that "trade in demo account can win, but trade in real account cannot win". Risk levels are different in demo and real account due to
ownership condition are different.
He yet to understand you from your example of situation and still repeat the same question ''not sure how they trade demo and still 'create profits"....