… I’ll Hold ‘Em Off says: You win if you are the only player with a zombie creeper and you have the Shotgun or any other Keeper that can be used as a weapon.

A: It is not required that you be the only one with weapons, only that you’re the only one with zombies. Think of it this way:

We all might be armed, but you’re the only one actively fighting zombies, since they’re only in front of you, so you can claim to be stepping up as the big hero. If you had a zombie, but no weapons yourself, of course, you’d hardly be “holding them off”. In fact, you’d probably be getting your brains eaten.