"Had he bullied someone on the internet (I mean targeted someone in order to cause emotional harm), I would understand and agree with the ruling."

From my understanding of the situation (having read the OP) that's what he did, though. =/ And if his intent wasn't to cause harm? Then he should have backed down once told that it did cause harm. If you drive recklessly and kill someone, you get in trouble even though you didn't "intend" to hurt them.