No. What is stupid are the teachers. They could have just taken the knife and sent a note home to the mother telling her of the policy.
Good god to call the police and have her arrested - thats what is stupid.
Do you think the administration would back the teacher for exercising common sense? The teacher is required to report, then the administration would call the police.
I agree the policy is foolish in its inability to make distinctions between things like this and serious threats.