http://pol.tasb.org/Policy/Download/367?filename=FOD(LEGAL)....
These are the relevant documents. They are short enough to read them in less than 5 minutes. Can you tell me what the legally-mandated punishment is for bringing a non-weapon that resembles a weapon onto school grounds is?
It's easy to bikeshed about "characterizations", but there are legally no other ways the school district could have reacted on the day they were making decisions.
Can you explain the relevance since -- except in the sense that every digital clock in existence resembles a fictional weapon through the Hollywood tendency to depict bombs as digital clock displays -- the actual device in question does not in any meaningful sense resemble a weapon.
Further, you answer your own question.
Remember that chicken fingers qualify as weapons under these policies.
Zero-tolerance policies are their own can of worms, but neither such policies nor any possible explanation of their enforcement explains the characterizations made after the fact by both school and law enforcement officials regarding the supposed "hoax bomb".