They were too fast, and he was mentally slow, but when he walked out he had flashlight or something shaped like a full sized pistol in his right hand. Someone clearly thought he was walking out with a gun.
But that was some big time amateur cop work. There must have been five separate cops yelling commands.
That was a robot which the cops had just thrown inside. He picked it up and walked to the door with his hands up - with it in his hand. But, it belonged to the police. They had just thrown it.
Yep, sure can see whatever was in his hand being identified as a weapon.