I should mention that while the 2018 edition of IFC says that fire drills shall be performed monthly in Group E occupancies (i.e. education occupancies) per Section 405.2, drills shall be designed in coordination with local authorities per Section 405.1. Prior editions that your jurisdiction may have adopted may be different, or local amendments may change these requirements outright, as the I-codes are a consensus standard.
Putting on a “fire drill video” isn’t unheard of, as in Texas, there is a further requirement that there are to be two fire drills within the first two weeks of school, but one of these drills can be satisfied by either verbally or informally going over evacuation requirements.
This may have been coordinated with the local AHJ, so without knowing anything else other than “for this one fire drill they put on a video rather than making the alarms go off” may have actually been allowed (albeit reluctantly) by the AHJ. You have to remember that we are still technically in a pandemic and OP first posted this in February, in the dead of midwinter.
You can fault the AHJ for their lax/poor attitude toward code all you want, but like it or lump it, it is ultimately up to them how they interpret it. Unfortunately, if engineers and code consultants always had their way, the world would be run much smoother. This procedure is goofy to be sure, and if it were up to me I wouldn’t let them do it this way, but this very well may have been run by the AHJ with their blessing. If not, then the school district will have to answer to them eventually.