NAH. If anything, your school's probably the most in the wrong here for putting kids in a fire hazard situation. Personally I would've kept them turned on and been warm, just not sat too close to the plugs.

Anyway, it seems you were asking more about how you spoke and their response to you. I know you aren't intending it as asshole behaviour but it can seem like it to others. It can sound condescending. Lemme try to deconstruct your intentions a bit...

You knew the heater was a fire hazard, so you had to unplug them. You were worried that other people would be annoyed at you for making them cold (or that they might plug them back in, fire hazard!)... So you preemptively explained the reasoning to them, since they might not be aware of the fire hazard label. I guess you added the "be dead or a little chilly" as a joke, because you worried about being taken as an asshole and wanted to try and lighten the effect a little bit?

Am I close?