This is of course entirely possible. But I can't imagine what they would find since he has the full balance as available for withdraw, no bonuses were used or are active, it wasn't a promotion, and crypto was used on a probably fair casino that's been around since 2014.
And yes I expect them to request a testimonial etc.
They might accuse your friend of multi accounting. I don't know why but they could do it i've seen users being accused of it and the casinos won't show any proof so they could cheat their way out.
If I am not mistaken, I have seen plenty of dice sites here process withdrawals of 10 BTC or more to winners. No questions asked. These are sites with extremely basic information required to sign up in the first place. MoneyPot when they still had the lottery jackpot, if I can recall, just let the user withdraw all 30 BTC that was won back then.
Back then the price wasn't high but yeah there are still casinos that process big withdrawals within less than a day. I guess it depends on the casino since 7bit also accepts fiat deposits verification is a must for them.