Yes, the article didn't say anything about motive because the guy it said wasn't talking.
Did he deserve a lead treatment at the instant the action was happening? Of course. Anyone nearby who was armed had a legal right to step in to save the boy's life. That aspect of things doesn't mean the attacker is a mentally healthy guy; just that he got lucky and no one did him in.
And of course any revenge taken after the threat had ceased would be criminal by itself.