If anything, it originally started as calling things "goyslop", which you might be able to deduce is a portmanteau of "goyim" and "slop", the implication (given it's 4chan) of course being that it's low-quality stuff made by Jews that is foisted upon the "goyim" (non-Jews). To the point that I usually see people calling it "AIslop"... specifically to differentiate it from "goyslop", so pervasive is the use of the term.
I'm honestly surprised "slop" (in this specific context) is hitting the mainstream (apparently) given it's so closely married to anti-Semitic undertones. I assume it's kind of like Pepe? People see the cute frog or the edgy designation of things as "slop" not knowing that's kind of a minced version of how it's actually used on 4chan.