I'm guessing they are referring to a certain synonym for idiot/moron/imbecile/cretin/dolt/etc. which fell off the euphemistic treadmill

That would be the “Linus Sebastian misconception”

Ok, but I can't possibly be the only one who has no idea who that is, let alone what misconceptions they have.

Yeah, that's the Linus "hard R" (he thought "hard R" referred to "retard"), but it's just wrong. "Hard R" is "nigger", in opposition to soft r ("nigga"). I don't think there's even a question, that's how hard/soft has always been used. Anything else is just confusion, I think.