A dog biting and breaking the skin is not much different than a bird biting and breaking skin. They are animals that we chose to domesticate. No matter how much time elapses, they will still have wild tendancies. Just like a bird, you must watch and know the dogs body language. A dog will not bite for no reason at all. The reason may not be completely apparent to a human, but there is always a reason. That being said, the dog should have been on a leash. It's upsetting that the owner was not in control of his dog and that this happened and he is so seemingly unfeeling about it.
My brother was attacked by a labrador about 4 years ago. He was with his dad at a friends house and had been standing there petting the dog. He went to bend down to the dogs level and the dog attacked. This was not my brothers fault, by any means, but the dog, for whatever reason, felt threatened and bit him in the neck and face. My brother was rushed to the ER where his wounds were irrigated and stitched. The scars are thankfully very faint now, but the memory will always remain. The dog was taken in by animal control and kept for a 7 day observation where he was temprament tested and the owner had to provide proof of current vaccinations. Upon successful completion, my brother was called into the judges chambers and asked how he felt about what happened to him and what should happen to the dog. My brother said that he knew the dog bit him because he felt threatened. He asked the judge to release the dog back to it's owner because it had passed the temprament testing. The dog went home and has never bitten again.
Now, with all of that out of the way... why is it acceptable for our birds to bite repeatedly, but not a dog? Would you put your bird down because it drew blood on a stranger? Nope, I didn't think so.