As a nightguard at freddys, you've seen some weird shit. But you've never seen a normally aggressive animatronic act in a non-aggressive manner.

The 'normally aggressive animatronic' in this situation is withered bonnie, who was in the parts & services room alone when you went to inspect. He seemed.. curious. Looking down at you with his red eyes. "Nightguard." He observes, stating the obvious.