Mmmm can someone explain to me what the amount of weapons really matters?
Obviously the kid had issues, and he was caught prior to any damage being done, but I can cause as much mayhem with a .223 hunting rifle as anything there.
I'm also willing to bet the grenades were defused and the story doesn't say.
So the kid had a bunch of swords, air guns, one real gun which is no more dangerous than a rifle and 'grenades' which were most likely not live who may or may not have had planned to carry out a school shooting and didn't have ammo for his one firearm.
Ah well it does make an impressive looking picture though.