This case seems pretty bizarre. Imagine the scenario where a teacher and student are arm wrestling. The students jump in to pull back the arm of the teacher and then one of them claims the teacher bit into her arm. A person's face is often close to their arm wrestling hand while doing this. It is not hard to imagine 4 or 5 other hands and arms in the mix and then one arm is strafed across the teacher's open mouth. The students were over the line, jumping in, but that is beside the point. A man's entire career is on the line because there might have been some tooth marks in an arm for a few hours. This is my "biased" guess as to what happened.
I find no sense of proportion in the justice of this event. As a teacher, one feels plenty of pressure from the students to liven things up. Good teachers break up some of the monotony with events like this sort of thing, rather than barreling through academics, ad nauseam. Then something like this happens and the Monday morning quarterbacks come out and explain the pitfalls of this behavior.