IP addresses and phone numbers can be spoofed, so it's hard to say where this is coming from, but the level of coordination indicates that someone is being systematic.
The fundamental trauma for parents of kids at any large school (likely leaning more liberal, the larger the city) is the goal, as far as I can see, with softening up resistance to gun bans part and parcel of that.
But to have such an event at a High School where I recall seeing the pickups parked (well, at the old school, this building is newer) with loaded rifle racks in the windows and no worry of theft, either, is a real change, and will register even with the parents who grew up in the area first as fear for their kids, and possibly as misdirected anger toward people who own popular firearms instead of those who perpetrated the hoax and possibly placed lives in jeopardy--even though those pickups with the rifle racks full back when may have belonged to them.
The idea that 'it won't happen here' is being chipped away at.
Hopefully, here, at least, after the inevitable relief their kid is OK, people will just get angry because some jerk cost their kids another day of school and endangered them to pull a 'prank' that may have more diabolical roots.