That's really unfair, and I'm sure he gambled at a casino that has a bad reputation, and I would ask if there are measures to just make sure that it is a trusted casino by looking at its reputation first before he finally decides to bet at the casino? If not, then that's the consequence that we don't get justice when we are really lucky by getting a lot of lucky wins, even though the casino promises to pay it but if it takes a year to be able to cash out the winnings then I think a gambler will still feel disappointed.
On the other hand despite everything I think it is really a very concerning situation and surely he is very disappointed with the service of the casino, because the casino should behave fairly which is simply that if there is one gambler who has won a lot of consecutive wins then the casino should have a good responsibility to pay the gambler according to the amount won and at the right time without any delay in payment, especially in that case he did not commit any fraudulent acts at all. In conclusion, I think this incident can be used as a lesson for gamblers to first check the reputation of the casino to ensure that you are involved in a trusted casino.
I also don't think it will happen in big casinos like stake. And the amount was not so big either. So why use a small and not reputable one if you don't want to have issues like this, I am just assuming a small one. The OP said, he is a friend of his. Since he is promoting stake, why not introduce him to stake because this casino can handle huge amount of money. Just look at the amount Drake is betting on this site.