This case has absolutely nothing to do with the First Amendment.
A student in my fifth grade class was suspended from school for a week because he called the teacher a "****ing b****."
Were his First Amendment rights violated? After all, he was just expressing an opinion.
Is she?
L
Actually is does. I am assuming your fifth grade classmate (or student) tarred the teacher with the epithet in class. In this case, the disruption of the class—there being a state interest in universal education—was the basis for disciplinary action under the prevailing First Amendment jurisprudence as applied to schools.
In this case, there was no disruption of education: a work of fiction was seized by a state functionary, and used as the basis for a state-imposed punishment.
The state claim that the story constituted a threat very much involves First Amendment jurisprudence, as there is a body of case-law dealing with what speech (or written expression) is, in fact, not protected by the First Amendment because it constitutes a threat (’true threat doctrine’).
The case thus involves the boundaries of what is protected speech or writing under the First Amendment, both boundaries set by the state interest in universal education, and boundaries set by the non-protection of true threats.