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.