The movies get silencers very wrong... It would be a bit louder than the acorn and sound much different (or about the same volume if the vehicle is really well soundproofed). The officer should have known immediately that it wasn't from inside the car. If it was a downtown area where stray bullets are an actual threat, I might have gotten down and scanned the area for danger, maybe radioed the possible stray bullet and assessed vehicle damage after a couple minutes. And that's just common sense, I have no real training whatsoever. But literally any kid who's gone squirrel hunting knows better trigger discipline than that.