Here’s the Texas Penal Code definition of a “Hoax Bomb”. Chapter 46, Title 10-, section 46.01.13:
That’s a lot of wiggle room for the authorities. Who can say what “reasonably appears to be an explosive or incendiary device”? (Would any random PC board hooked up to a battery and LEDs qualify?) And damned near anything can cause “alarm or reaction of any type”
You could, then, say that the school officials were arguably within their rights to call this a “hoax bomb” and in taking action. That doesn’t mean it was at all intelligent ort advisable to do so. And calling it a “hoax bomb” is a loaded phrase that needlessly puts the onus of wrongdoing on the student.
http://www.statutes.legis.state.tx.us/docs/PE/htm/PE.46.htm
Massachusetts law, in my all-too-quick survey, seems to be more rigid, stipulating that an offense exists only if the hoax device is used with the intent to cause “anxiety, unrest, fear, or personal discomfort.” So there wasn’t any reason to charge the MIT student.
https://malegislature.gov/Laws/GeneralLaws/PartIV/TitleI/Chapter266/Section102