"DNS wasn't around in the 1970s. And neither was vi or emacs. The 70s and early 80s Arpanet used the hosts.txt file."
Not as DNS, no (that was 1983) ... But there were (localish) implementations of name to numbers translation that mostly worked.
I think you'll find vi & EMACS[1] were both born in the same year, that year being 1976. I remember swearing at Bill Joy in person over vi, and at rms via email over EMACS, both well before 1980.
The first copy of Jake Feinler's file that I received from Jon was called HOSTS.TXT ... yes, all caps. It was renamed to hosts a couple years later. The Hosting Name Registry started in 1972.