I mean, given enough time, just a mere salary man can become a millionaire (and with more time, a multi-millionaire) only by keeping their spending low and stashing the rest of their net salary into index funds. Sure, that’s capitalism which isn’t too popular in Lemmy, but it’s just an example of how a millionaire can really just be a normal, somewhat frugal, person. They aren’t showing their wealth though because that’s the reason they are able to save such a nest-egg so you can’t really tell if your neighbor is secretly wealthy or not.
Billionaires (and “multihundredmillionaires”) are a completely different group of people though, and no normal person is able to amass such wealth without a shit-ton of luck and most probably some abuse as well.