alex,
I never heard of penalizing a player in a cash game. It would be unethical, to intentionally announce a "bad hand," only to expose a more powerful hand. As Mike stated, it could be accidental. However, we must let players know that what they say at the showdown is meaningless until the cards are properly tabled. Remember, "verbal is binding" only pertains to amounts being bet or raised, not considered binding when announcing the contents (or rank) of a hand.
The odd part about this hand is for Player A to table his hand. Usually, when a player misreads his hand, or thinks he is beat, he simply mucks face down and that's it. Verbal means nothing at showdown, so I encourage dealers to insist that players follow these proper rules of showdown: Show your complete hand before looking to the next player. Example: Player A says " I have Aces up" before anyone else reacts, I will ask Player A to please show his hand. "I believe you but, I must see them." Then you can move to the next player.