What a bad timing indeed. Honestly, there was no problem at all on the side of OP, regardless of whether he was using a casino address or from any wallet since he always checked the deposit address no matter what when doing a deposit transaction.
I agree, it's should be honored by the casino if that address is designated to OP's account. They can always verify and recover funds that are sent to that address because they have no prior mentioned announcement for that change.
He did the right thing of checking his deposit address first which is a norm for each of us before doing any transaction.
It is that the situation startled by the casino for doing some updates and there's no need to argue with that if a user used the old address and they have made that update just a few minutes ago after the transaction was done.