Rust could also be short for "Rustic"
rus·tic
ˈrəstik/Submit
adjective
1.
of or relating to the countryside; rural.
rural, country, countryside, countrified, pastoral, bucolic; More
antonyms: urban
derogatory
lacking the sophistication of the city; backward and provincial.
"you are a rustic halfwit"
synonyms: unsophisticated, uncultured, unrefined, simple; More
antonyms: urbane, cultured, sophisticated
2.
constructed or made in a plain and simple fashion, in particular.
Or it could be RUST as in post apocalyptic which is what the developers said they were going for in the first place. RUST was a dayz clone from the start. I actually think its a good idea to rename it to something like Rustic. Good idea.