The police are responding to the public's needs, so they will go by what information they have at the time of the call.
So in your case, the police have got 2 dogs fighting in a public place, children and other dogs present. Here you have the publics safety to think of first, i.e children incase there are dogs that are fighting, not in control, and not on a lead.
I can see your anger, but like you said there was no fighting, just your dogs PLAY fighting. To the publics eye they obviously see 2 dogs (the breeds of dogs) which looks like they are fighting, so they call the police to de