Guess you make it wrong already.
For your friend case, it is coming through the phone line. Happen to me twice. I'm using lower rating ELCB.

Is it? So signal transfer using optical don't have current
Fiber optic or copper, it is just used to transfer data. And you need current to transfer data. You no need to have much, just extra 10-20A surge are more than enough to fry your appliance.
And if that extra surge of current are really going through electric pole, the damage done won't be just unifi equipment only. You will need to change 50% of the house appliances.
Use wireless modem and don't use network cable.
Now Streamyx TM improve the system already, their junction box now comes with auto reset ELCB(think unifi don't have yet), whenever there's thunder storm in my area, I sure can't go online. And once over, I can use it back.

Still, it need to do conversion, right?