It's interesting how gameplay tropes lead our behavior in games, frequently. Most players know to shoot what's in the room just because they're closed in with it; it must be a boss, it must be evil, it must be killed, on the basis of context rather than any objective knowledge.
Faced with something that isn't overtly trying to attack HIM, it's neat to see someone react with "what do I do"? instead of immediately blasting away.