I'd agree, except that does not apply in this case. Since it already happened to his child, it would be logical to assume that the odds of losing his child is greater than 1/7,000,000,000. Keep in mind that it's not only to avoid a headline-grabbing abduction, but any prolonged loss of contact. They may say his child was never in danger, but that is small comfort when you have to spend hours searching for your child after the school calls and asks why your he/she is absent.
I can also sympathize with the submitter not seeking a solution that depends on the school. Although that might seem a reasonable thing to do, after talking with them, he probably got the impression that they don't think they did anything wrong and would need to see multiple repetitions of this error before taking any corrective action. Parents are a school administrator's #1 enemy - expect to be treated as such, unless they're trying to get money or volunteer work out of you.