I was walking my 3 dogs with a small dog following us for 2 blocks, barking behind my dogs. One of my dogs attacked this dog. Am I at fault?

I just returned from a walk with my 3 dogs very shaken up and would like your advice. At the end of our walk, about 3 blocks from my house, a small (approximatly 5 lbs.) dog ran out of its house and started barking at us and yipping at our heels. I yelled at it to go away, but it wouldn't, and followed us for a couple blocks. I stopped to look for rocks to throw after it was apparent it wouldn't leave. All 3 of my dogs had head collars on (Halti brand) and one of them went nuts as this dog was barking. I have a German Shepherd and two mixes, approximatly 70 lbs. each. My 3-year-old mix, who has never displayed aggression towards another dog or person, went nuts and as I was pulling him onward, wrestled his way out of his head collar and went after this small dog. After about 30 seconds, the dog owner came out of her house and ran down the street and got her dog away from mine. I was yelling for help, but that is about all I was able to do because I was afraid the other two would join in if I got too close. My question is, Who is legally responsible in this case? How can I train this dog to refrain from attacking, even if provoked? Or is that a pipe dream? Thanks for any advice you can give.