Even if there were two dogs fighting, when a human chooses to insert themselves into an animal fight, they become part of the fight in the minds of both animals. Dogs do not reason like humans and just because you think you know a dog and the dog knows you does not mean they will not perceive you as a threat in a fight. People like to treat pets as if they are people or kids and while most of the time, they will play that role willingly, there are times they only see you as another animal and potentially a threat.
My family had a big dog when I was growing up that was friendly and loved people. If you raised your voice, he would cower down or back off. However, if you ever tried to get near his food, he would growl and snap at you. As soon as you took a couple of steps back, his tail would start wagging and he would become playful again.
Hopefully the truth or facts will come out about this story long before something is done to the dog.