I bet the dog ran afterward and the owner went after him. This is just so sad and not your fault at all. Was a large dog? Something similar happened to me many years ago. The dog ran home and I went to the door to tell the owners that I had hit the dog. He was sitting on the floor in their living room like nothing happened. I was in tears and had 6 kids standing with me at the door to this house.
You did all you could have possibly done. I'm so sorry