I read the article. The 911 operators hung up when they were told that the cops were there. They should have explained WHY they were hanging up, but the bottom line is that the 911 operators’ job is to send cops, fire or ambulances if they’re needed. If the cops are already there then there’s not a lot that the 911 people can do. Once cops are on the scene it’s their job, not 911, to assess the situation and call for backup.
I generally agree with that statement but there can be times that it may be appropriate to call 911 if you see the police in over there heads in a situation.