So... kid with an Arabic name, whose father is a belligerent Islamist known to the townspeople to rail against imagined anti-Muslim racists in the town square, shows up at school with a homemade electronic device with a timer on the front of it. He takes someone's bad advice to conceal it under his clothing, and walks into a classroom where it starts beeping.

I think reasonable people can understand why the police might have been called.

It was of course unreasonable for the police to have actually arrested the boy, once they found out what they were dealing with. Reading between the lines though, maybe the article's use of "arrested" just means they took the kid home to his parents.