No, that is wrong. There are certainly cases in which the implication does not hold true, e.g. if the player abused a bug in order to win the game. Not to say that this was the case here, but the implication does not hold. They should have returned the deposit ages ago, then handle the dispute but only regarding the winnings, which is what would have been far more acceptable to me.
I mean if there is some sort of tampering it would still be Cloudbet's word against his. No one can prove if that happened or not. So if we settle on the middle ground where both parties agree, OP and Cloudbet both know the deposit address, and they both agree the winnings are valid from whatever bet OP did.
OP still didn't sign the message from the deposit address, and ignored my PM a week ago when I told him to do so to prove his point. We're all only hearing half the story, but if he does indeed still own it then it's pretty much case closed in his favor. And Cloudbet just wants to waste more time.