So "terrorist threats with nothing to back it up" aren't necessarily worth 8 years in prison, but terrorist threats could be, under maximally aggravating circumstances. Say you were an actual terrorist going to great lengths to make plausible threats in order to terrorize the populace.
Remember that terrorism isn't about bombing or shooting or killing. As Bruce Schneier said, "Terrorism isn't a crime against people or property. It's a crime against our minds". Making threats is the crux of terrorism.
What's ridiculous is charging a kid who clearly wasn't making the kind of serious threat that these laws were intended for.
(I'm making some suppositions here - my case would be stronger if I had dug up the actual laws and charges.)