“Why didn’t the kid just drop the gun when he was ordered to do so by police?”
It wasn’t a gun. Why don’t you get that? So when ordered from behind to drop the gun or the weapon a 13 year old might well have not know what the cop was talking about or even who the cop was yelling at. He might have even turned around to see who was yelling.
It looks like a gun, fires projectiles like a gun, is regulated like a gun, and was the only object in the teenager's hand when the police approached him.
What the command 'drop the gun' meant in this instance is prima facie obvious and not really open to the type of insipid semantic interpretation you're attempting.