Hi
Hope you are both okay, must have been a horrible situation. Firstly regarding the dog fight, I'm afraid you are both as responsible as each other in this situation. Both dogs were off lead and therefore not under control so legally there is nothing that can be done or achieved by reporting it. I suspect your dog did provoke the attack by his body lanuage and your GF grabbing his collar would only make matters worse. It's an automatic reaction to grab the collars but not always the best thing to do as it can highten an already unconfident dog to a state where he feels forced to attack. Fight or flight remember is a dogs defense so if he feels he can't escape he will attack.

But I would most definately report the attack on your GF, although I suspect it will be very hard to prove who threw the first punch or who provoked who but it can't be left and does need to be reported as those people are obviously thugs.

Invest in a long lead (not one of those awful retractable one's get something more like a horses lunge rein), then you can let your dog have a run but still keep control.