It's possible for the blind kid to have started the conflict by some sort of emotional abuse or something, but consider this:
If that relationship were a long-standing and one-sided issue between these two, other students who knew them would probably not be reacting to this situation the way they did. I can have some sympathy for a self-defense argument in the case of long-term emotional abuse, but that just isn't what this smells like. Add that the person's own claim on twitter is that he didn't know the kid was blind, and in my opinion, that interpretation is done for.
If there was not a long-term issue between the two of them, then reacting to the immediate situation with violence was wrong, and the guy should have expected stitches as a potential consequence when he put up his fists. Whether those stitches came from the person he thought he was fighting or someone else intervening doesn't really have any ethical bearing on the value of the "bully's" actions in this case.
Now consider that the person who intervened knew that one of the participants was blind. If he was just entering the situation, without knowing how it began, it would be perfectly reasonable to assume that a blind kid caught in a fight is being subject to bullying. It would also be common sense to realize that the blind kid is in much greater danger of much more serious harm than his opponent. The blind kid won't have the same awareness of his environment. If it was the blind kid who took a fall, it would have been likely to result in more serious injury than what ended up happening. It makes sense to want to end the situation as quickly and effectively as possible.
Rolan, I'm especially surprised at you. In our debates on police violence, you've taken the stance that responding to a violent threat with a higher level of force is acceptable, and if I remember right, you're one of the types who will argue that an unarmed person can be surprisingly dangerous and close distances quickly and that's why it's ok to shoot them if they show any sign of aggression... but here we have an actual physical fight fully in progress, and your sentiment completely flips when a police officer isn't involved.
Finally, I dealt with some fairly serious bullying for several years of my childhood. It would have been huge -- HUGE to me on many levels if anyone had ever stuck up for me the way that guy stuck up for the blind kid. That would have rocked my fucking world.