Recieved a 10 and a joker at the DD game at the Mirage

Funny thing happened the other day at the Mirage in Vegas DD game.
on a $50 bet I get a 10 and joker. I say yay I got a blackjack, I want that joker to be an ace. Dealer calls the boss over and he says I can call that a blackjack and get paid 3 to 2. then they take the joker away. Thinking back on it I could have made more money by doubling down if the boss let me use that joker as a wild card but I'm happy he didn't call it a dead hand. I don't know how that joker got in there I thought they check the cards before they put them in play.