I agree with everyone else. I would hope the owners of the dog would step up and pay the bills without any issues... I don't think you did anything wrong!

I had something similar happen what about 13yrs ago... I was walking my first Collie, who was barely a year old... we were walking around the high school football stadium when this guy with a Golden showed up with his dog off leash.. he was on the complete opposite side of the stadium but his dog saw mine and came charging around after us. The owner of the Golden did nothing more than walk around to get to his dog, he was in no hurry... of course by the time he got to his dog, his dog had already jumped on mine (I was 12-13yrs old at the time) and knocked him down a few steps, and though I didn't know it at the time, my dog had got bitten a couple times on the hock. I couldn't break it up myself, plus my dog wouldn't let the golden near me, he kept himself between me and the other dog.... by the time the owner got there the dog stopped attacking mine... the goldens owner asked if I was ok, didn't ask about my dog... and said his dog just wanted to play.. leashed him up and left...

As I was walking home I noticed blood running down my dogs back leg... vets were closed so we took him the next morning... it was nothing major but he was sore for a few days and limped around for a few days.

I didn't know who the Golden's owner was though... but by talking to a few other people in the general area, who have had similar issues with a Golden going after their dogs, we got the name of the possible owner and tracked him down so he could pay vet bills... took a couple weeks to finally talk to the guy but he paid the bills...