Don't be defeatist. The situation under consideration here is probably monitored by security cameras and body cams end to end. Everyone not following correct protocol did so on camera. Punishing willful ignorance and incompetence is certainly possible.
In this case, the kid was holding the clarinet like a weapon, and though we have not seen the actual video, the descriptions of it make it sound like overall resolution was poor.
The alternative to the false positive here, is to not report anything that you cannot be 110% certain of, which means that you're likely to miss some true positives.
Overall this situation mostly reads like everything worked as intended, and the press turned it into more than it needed to be. School shooting are a real thing, there is plenty of evidence of that. Weapons detection has become a necessary component of a school safety strategy. For many reasons, it is not practical to have personnel at the school, or within the district, act as the first-pass reviewer of AI detections of weapons.