The core definition for a terroristic threat seems to be a threat made that may result in the evacuation of a building or area (i.e. a bomb threat, or conceivably a threat that you'll be coming to work tomorrow with a bag full of guns). Nobody previously responsible for these kinds of threats - kids trying to shut down their schools, the Irish Republican Army, et cetera - has ever issued them by means of oblique Webcomics, creative writing assignments or LED-lit signs resembling Aqua Teen Hunger Force characters, on account of how that would be a completely stupid way of threatening someone.

This fact does not appear to concern the offices responsible for arresting people for having done such things. This is because War On Terror statistics appear to be front-loaded, like Enron's accounts. You get paid based on the arrests you make, not on whether any of those arrests even lead to a trial, much less a conviction.

Every time a kid's thrown in jail for writing a story about zombies attacking his high school, another gold star goes on someone's curriculum vitae.