No idea that was actually a thing for people. I thought it was something "left behind" in evolution which is why I thought it a good insult... But this context makes it HARD in the ableist category and the interpretation makes it eugenists, yuck!
Dirt person is just something I picked up in the military. We would refer to the state side civilians that lived in the area around our base as dirt people. Pretty elitist (I was a fashy prick, we all were). But I use it now as a parallel to "bog dweller", a slur for Br*tish people. I've always thought of it as Brits/anglos being willfully ignorant and feeling superior by choosing to live in bogs.
It works just like an arms race. If you want really secure, use offline devices. Microwave your electronics if you want to destroy everything. But even better, hand written single use short cyphers.
99% of those people aren't ready in the least for what that means...