This is puzzling. I'm not going to comment on the context that you all have adequately talked about. I'm going to try to answer the question that the OP is asking, which, I believe, is what were the grounds for the disfellowshipping and upheld appeal.
If the girl had been killed outright, then if it was clear that OP was negligent in having dogs that are known to attack people such that OP knew or should have known that the dogs were dangerous, he could be disfellowshipped for manslaughter and the associated bloodguilt.
However, here we are talking about a near-death. The girl could easily have died but did not. She was gravely injured and was severely traumatized. So the grounds mentioned previously would not apply specifically. If, though, the elders met with OP and discussed the situation and it became clear that OP knew or should have known that the dogs werr dangerous AND OP defended this and showed wanton disregard for the value of life in this case (as his comments here seem to indicate), I would think the elders would have a good case to disfellowship on the grounds of "brazen conduct". To be clear, the bad attitude about disregarding safety and the value of life would have to be extreme before disfellowshipping would be justified, in my opinion.
Are these comments helpful?
CC