The origin for computing is actually documented too.
The term daemon was coined by programmers at Massachusetts Institute of Technology's Project MAC (Mathematics and Computation) in 1963, inspired by Maxwell's demon, an imaginary agent in physics and thermodynamics. In a thought experiment devised by James Clerk Maxwell in 1867, a demon would control a small massless door between two chambers of gas, forcing fast-moving molecules to pass through in one direction and slow-moving molecules to pass in the other direction. In Greek mythology, a daemon was considered a supernatural being or power.
https://www.techtarget.com/whatis/definition/daemon
There's also a response on Virginia Tech's website from a professor from the group that used the word first.
Your explanation of the origin of the word daemon is correct in that my group began using the term around that time frame. However the acronym explanation is a new one on me. Our use of the word daemon was inspired by the Maxwell's daemon of physics and thermodynamics. (My background is Physics.) Maxwell's daemon was an imaginary agent which helped sort molecules of different speeds and worked tirelessly in the background. We fancifully began to use the word daemon to describe background processes which worked tirelessly to perform system chores. I found a very good explanation of all this online at:
I also found this stackexchange post that adds even more context to it.
