The things is - you can't actually know for sure - it is entirely possible to get covid and have nothing more than a sniffle or nothing at all - so I think what the OP you are responding to is saying is that just because someone thinks they never had covid, it might not be true.

I know people who never had symptoms, but tested because a household member had tested positive (with symptoms) and found out they were positive too - it happens.

In my opinion, that is the best case scenario - you got it, didn't know it and your body fought it off like a champ.