Bad dog....bad owner.
I don't think we have evidence to draw this conclusion at this point. There was a bad outcome, but so far we have no evidence to suggest that the dog had ever done anything that would suggest that he would be aggressive towards a child. If a parent makes a mistake that causes an accident and kills his child in the back seat, neither the accident nor the mistake mean that he is a bad driver. Often, tragedy happens because that one in ten thousand bad outcome comes true.