If you believe that sometimes, gamblers can also win the casino, kindly drop all the explanation of why you have such a believe.
In my opinion, depositing $50 and withdrawing $500 can be considered winning at the casino.
Winning at the casino isn't just about winning a life-changing amount, but also about withdrawing more than your deposit during that playing session, even if you're still in the red or only have a small profit overall. Winning at the casino for a huge amount is something very few people have ever experienced.
Yes, this can also be a sort of casino winning, and in major cases, propels are going in this sense. However, here I think the OP is talking about that one big win which can make a person wealthy in a way that they don't need to play and type of gambling anymore. In your case, we can't say it's a casino winning because the amount he wins in the casino will be lost by him again and again in that casino. It can be motivated by luck or just by skill, and he may lose it again. The casino winning will be considered when he bets 500 dollars and gets 5k dollars, and then he quits the casinos and does not play for the rest of the time. But it's nearly impossible because the casino odds and algorithms are designed in a way that he has to play some other games until he loses that again.