Miscalling your hand during showdown is covered by Section 1 (Poker Etiquette) of Robert's Rules of Poker, and is grounds for warning, suspending, or barring a violator:
- Making statements or taking action that could unfairly influence the course of play, whether or not the offender is involved in the pot.
Additional rules applicable to miscalling hands during showdown are in Section 3 (The Showdown):
- To win any part of a pot, a player must show all of his cards faceup on the table, whether they were used in the final hand played or not.
- Cards speak (cards read for themselves). The dealer assists in reading hands, but players are responsible for holding onto their cards until the winner is declared. Although verbal declarations as to the contents of a hand are not binding, deliberately miscalling a hand with the intent of causing another player to discard a winning hand is unethical and may result in forfeiture of the pot.
In the OP's example, the casino clearly has the authority to both 1) bar the offending player, and 2) award the pot to the player who discarded his hand as a result of the offending player's illegal action.
EDIT: I voted "angle", and feel that the player was justified in calling for a floor ruling (who then got it wrong). In nearly all cases, it is in the best interest of the game for the best hand to be awarded the pot if at all possible.