Flat out murder would be difficult to argue. If either premeditation or proper mens rea had been proven, I doubt the case would have been dismissed. Manslaughter seems like a somewhat more appropriate term though, with some allowance for both the kid's age and what sounds like a lot of previous (long-term bullying) and immediate (being followed partway home and then punched in the back of the head) trauma. Plus whatever additional charges for carrying a concealed weapon. Then again, I'm thinking of Canadian law and I don't think we have an equivalent of "Stand Your Ground." We do have self-defense clauses in most of the assault laws (I'm pretty sure. I'm not a lawyer).
Emotionally/morally/intuitively though, I can simplify it down to this: it's not ok the one kid was bullied. It's not ok the other kid was stabbed. Nothing about this situation is ok or justifiable or deserved. Much as I'd like to feel better about the situation because it was resolved or through rationalizing awful behaviour from one of two messed up kids, this is not a win on any level, just a crappy situation that ended horribly.
Emotionally/morally/intuitively though, I can simplify it down to this: it's not ok the one kid was bullied. It's not ok the other kid was stabbed. Nothing about this situation is ok or justifiable or deserved. Much as I'd like to feel better about the situation because it was resolved or through rationalizing awful behaviour from one of two messed up kids, this is not a win on any level, just a crappy situation that ended horribly.