They're right. Slop being an actual word used in common parlance does not explain its connection to media or AI. "Goyslop", which is often used in shortened form as just "slop", has a huge presence on 4chan. "AI slop" was first used there back in 2022, and it's grown in usage since. Using the word slop specifically about media and AI in particular would have no cultural penetration if not for 4chan, and, by extention, /pol/'s "goyslop". Although 4chan's influence on online culture isn't what it used to be, it's still notable. You'll find tons of people using "goyslop" on twitter, for example.

No, and your post disproves it. The term is well older than 4chan and the relevant noun meaning (the "semiliquid food" sense) dates back to 1650: https://www.etymonline.com/word/slop I'm not sure if that encompasses "pig slop" which is what this is really tapping into, but that has been around at least my whole life and I'm older than 4chan too.

I assume the comment was deleted for pointing out it’s a sterilized version of 4chan’s “goyslop” which refers to meritless, poorly made, post-Obama modern media like what you would see on Netflix, and not AI.