Munchkin Booty (Not So Fast, Me Bucko!)

[MunchkinMan]

Canceling a Monster is an odd occurrence. Just about anything else, not so odd. I think the further implication that you're concerned with is that if you find a Monster and it gets canceled, you can't play one from your hand either, based on the wording of the card. Either way, your friend was correct to continue on with his turn. Canceling the card he just found kicking open the door in this case doesn't mean he should have to kick open a new door.