The suspect in the car was known to have at least one pistol with a suppressor. That being said, the guy was given a cursory pat-down and could not have had a suppressed firearm on him unless it was in him.

A properly setup suppressed pistol fired from within a vehicle would be fairly quiet, but would sound nothing like an acorn bouncing off a car and you would know if you were hit.

He has no business being a cop if he freaks out when an acorn bounces off a car and taps his vest. Luckily the suspect was not physically harmed and the cop resigned. Hopefully the suspect gets a nice payout from the city.