How do you charge someone with a "bomb hoax" unless someone initially assumed there was an actual threat of a bomb? Can you just somehow jump straight to "bomb

How do you charge someone with a "bomb hoax" unless someone initially assumed there was an actual threat of a bomb? Can you just somehow jump straight to "bomb hoax"? Why do you need to call the police for a bomb threat you know to not be real? If I said something stupid like, "I have a bomb" and the teacher _knows_ I'm lying. The teacher probably sends me to the principal's office or maybe gives me a stern lecture about "misusing words" If he really did something that warranted cops being called why would the Principal need to threaten him with expulsion if he didn't sign a written statement coping to that fact? You either have him dead to rights on making bomb scares or you don't. I honestly don't know if his dad was the cause of him bringing that clock to school. But man if that's true, the dad must have read the school well enough to know they would try to arrest his son on something dumb.