In a tournament that is correct, showing your hand before the showdown effectively mucks it. I am surprised no one cut him a deal though, if your friend was a begginer and did not know the rules he should have asked for his chips back or something of the matter.

In a cash game the rulings are different, you can show your cards and they are not mucked, but I am not sure what the rule is if someone is still to act, it could be considered collusion.