I wouldn't be surprised if they did it because he was tall and if he's gentle and kind, they probably thought it would be easy pickings.
But that's another problem. When a boy attacks another boy, and the victim defends themselves, for some completely disgraceful, sexist reason, it's seen as "fighting" where both are equally culpable.
If the victim doesn't defend themselves, they are told that they need to "toughen up". If they do defend themselves, well then, they were "fighting" and need to be punished. It's a disgraceful injustice and again, it can cause damage to the victim's self image and send very mixed messages.
