It's one of the more truthy backronyms. There was an actual ax man with an ax whose job was to cut a rope to let loose the control rods, and they did use the (existing, apt) word, scram, for the emergency procedure: https://en.wikipedia.org/wiki/Scram

None of this contradicts the point I was making, which is that the OP implied that’s what the term meant, and it simply isn’t.

Exactly what I would have answered :)