Update for my false alarm. Turns out a steam heating pipe exploded and I believe someone pulled it. If not the steam would have set off the detector pretty quickly.
The only school where I remember false alarms was my elementary school, other than one in high school on the last day of class one year. But in elementary school, there were some years where we’d have multiple, and usually right in a row (whether copycats or the same person). And, there were only six pull stations in the building (by code, I believe there should have been more, but…old building), so it’s not like there were a lot of places to do so. The high school was a very large building, with lots of hidden pull stations (meaning away from where people usually were), but it was quiet.