It's not the first time I have heard that something like this has happened, there have been stories about things like this before. But such a thing has never happened to me, and I have used many exchanges and have zillion transactions from exchanges to gambling sites and vice versa. And I don't know anyone who experienced something like this.
It is difficult to determine if something like this is really true... in exchange offices (as well as in casinos) people are often banned for various reasons, and people often "forget" to tell the whole story and show some proof. Maybe it's just that their account is connected to some other shady dealings but they decided to attribute it to transactions with the casinos.
I hear you. Things can get blown out of proportion, but there's definitely a history of exchanges taking action when it comes to gambling. It's a gray area, for sure, with legal stuff mixed in. If the original poster could give us more info – like which exchange, what kind of gambling, any conversations they've had – it would really help us figure out what's happening and give better advice.
For anyone else dealing with crypto and gambling, I'd recommend taking a good look at the exchange's rules and the local laws. Keeping detailed records of everything is also a smart move, just in case.