Scammy advertisement imo but if it's written in their terms that they can ask for kyc anytime, what we can do? It's what we signed up for. Read the terms, not the advertisement.
...or are they just using it as their own policy to forfeit players’ winnings?
If casino has mentioned, kyc can be asked anytime in their terms and upon completion of kyc they allow you to withdraw funds, it's fine.