Can someone explain the reasoning behind this serious charge to me? Please?

It depends on how you state determines what is a felony ault and how it is separate from what would be a misdemeanor. They may have new evidence that made it more serious. For instance, now you find out that he had injuries, this could make it a felony. Why the other guy got away with a lesser crime probably has something to do with a technicality somewhere. What state is this?