Joe, that's because it's a 911 hang up, not because they just show up any time 911 is called.
You're right, police haven't been issued mental telepathy, but the 911 dispatchers have been trained to dispatch. That means they make well educated decision on who to send in response to a 911 call. If they don't think there's a need for police on scene because there's nothing to indicate they're needed, they're not going to send officers. Last time I saw a cop show up for an injury was when a guy fell and hit his head. There was a question as to whether he was drunk, so the cops showed up. However, the medics determined the guy passed out due to medical reasons and his wooziness was because of a mild concussion, so the cop just radioed that to dispatch and departed. No report was taken because there was nothing to report from his end. The medics would write up everything that needed to be recorded.
