I flipped back thru my old Capers and all the adult shows not only said "Adults Only" but further specified the shows were for 18 and up and a few even said "X comedy shows."
I don't know how much more specific you could be, actually. On land "adult" entertainment usually means someone taking their clothes off......
I'm sorry you misinterpreted "adult" but at least now you know and can stay away.
As far as Carnival not having adult comedy, it reminds me of the obscenity arguments on dry land....no two parties can agree what is obscene and what it not. You did the only thing you could do - write your opinion on the comment card. If Carnival gets enough comment cards agreeing with you, things will change.