I know someone that said this to me about the pope, and I said basically the same thing: "he's literally the pope. That comment actually makes you the 'untrue' Catholic."
They say he's an apostate, and nothing you say will change their mind. What I recommend is not engaging in these discussions with close-minded people. No good will come of it.
I believe they're called heretics. Papal infallibility and divine representative positioning within Catholicism means disbelief in the word of the pope would basically be a renunciation of the faith.