Another example out of many: If my dad came home from work late and we starting eating without him the dog wouldn't let him in the back door. He would growl with teeth showing.
That's because regardless of what you thought, the dog was the pack leader and the dominant male. His reaction to your father was one of aggressive correction for whatever he felt your dad was doing wrong, for the betterment of the pack.
I have been reading a lot of Cesar Milan's books about dog psychology lately, and he makes a large distinction between aqggression and attack. Aggression is an applied state of mind by the dog, and should be corrected immediately so that the dog falls into place in the pack (family) and lives submissive and harmoniously. Attack is a physical, instinctual reaction to a situation wherein the dog feels his dominance is being threatened. A submissive dog will shy away from a situationand/or remain calm and a dominant dog will challange the threat (in this case the 5 year old) with a physical altercation.
I also have learned that dogs really could care less who is the pack leader, they just instinctually will follow a leader. That leader is not necessarily the largest, strongest dog, but hte one who can prove, through dog body language, that he is the leader now. The numerous bites this kid endured indicates that the attacking dog is the dominant pack leader at home (in his pack) and was threatened by her presence. Most likely he gave her body language warnings which she was unable to respond to, and since he most likely has NO training (I think it was mentioned that he was in a pen, so not really in a pack) and no experience in actually leading a pack, he reacted the only way he's wired to, attack. From the severity of the bites, it looks like this was more than a doggie-based correction. The dog need help, and the owner needs to get a gerbil, IMO.