If someone holds 1 bitcoin in 2023, can he call himself rich ?
That depends on the country you live at. If cost of living is high then the $30k/BTC isn't going to consider you rich. But in developing countries, that's a lot of money already.
If not, how many bitcoins holding is equal to being rich in your opinion ?
5-10 BTC?
If you consider yourself being rich with $100k+ of savings will you say that you're rich? It depends on what classification of yours for being rich. Someone can have a lot of properties and yet don't have bitcoin yet they're rich.