But "slop" has meant low-quality stuff for a very long time. See also "swill", both analogies to pig feed.

The earliest OED2 citation of "slop" for the sense "figurative. Nonsense, rubbish; insolence" is 1952. Slop was slop long before "AI slop" was coined, and AI slop is slop from an AI.

"Slop" originated on /pol/ but I'm not gong to try to tread the needle by of the rules by trying to explain it without being offensive or triggering some filter: The first related term here: https://en.wiktionary.org/wiki/AI_slop#English

You have this backwards, as Simon could tell you. In fact, Simon coined “AI slop” to mean “low quality AI output.”