So the boy in this story is hardly innocent, but if the story is accurate it just goes to prove how much authorities continue to over react to jokes and well, kids being kids.
Now here’s the thing, “plastic air-gun pellets” sound awefuly like airsoft ammo. Airsoft ammo is basically harmless unless it strikes you in the eye. Unlike paintball, it probably won’t even leave a welt when shot from an airsoft gun. The whole point of airsoft is that you can shoot your buddies, have fun and be safe.
Point is, other then some people freaking out by the “explosion” and getting hit by some small pieces of plastic nobody appears to be hurt (the story makes no mention of any injuries) and on face value, it seems unlikely that anyone would be hurt. So why the “weapons of mass destruction” charge? Disturbing the peace? Ok. Being an idiot? Sure. But clearly the kid isn’t some Al-Qaeda sleeper cell trying kill anyone.