To be fair (and I slightly hate myself for speaking up in their defence) the cops were claiming "bomb hoax", not "bomb".
Of course the police are also claiming "not racially motivated policing", so as we gauge their level of truthfullness we should keep both those facts in mind...
The police were not fearful enough to evacuate the school, yet made the claim that this seemed to be a bomb.
Explaining their actions without that context is a bit trite.