In tournament heads up, pot is 16000... river gives player A top straight who bets 4000, while Player B who has lower straight pushes allin 4800. Player A who has 5000 chips left thinks the bet is covered and reveals the nuts. As the dealer is passing the chips to player A, another player on the table disputes the decision because player A did not announce a call. After some deliberation with management, the decision to award the chips to player B was given. Was this the right decision?.
This was a terrible decision, and no competent poker floorman would ever have done that. The game is heads-up; a player has every right to show his cards at any time, and does not lose any privileges by doing so, because there is no third party to be affected.
The dealer should simply have reminded the player "you haven't called", and been allowed to call (or fold)--assuming his opponent still had cards.
If a player exposes his hand with action behind him. The hand is dead.
In this particular situation, there are 2 important things to note.
1) There was no more action left in this hand. The only decision left was from the player who had the action on him.
2) The hand was not exposed with the intention of inducing a reaction.
So, IMO, The hand should NOT have been mucked.