Am I the only one who sees this coming?
Also, there really hasn't been any jokes per se about Muslims at this point in the fake Family Guy episode. So the whole "only Jews can rag on Jews, Muslims on Muslims, blacks on blacks, etc" thing isn't really applicable.
Muslims is a possibility. Other possibilities:
the aliens that were using earth as a reality show
or to drive home the idea that Family Guy is just like Cartman the writers could be Cartman's dad (the Denver Broncos)
and we can't rule out crab people, we know they're behind Queer Eye