Is the Pope Catholic?

Yes, he is. Eric Muller seems surprised.

How degrading it is, at Auschwitz, to speak of Judaism as "the taproot of Christianity" rather than as the faith of so many who perished there! How presumptuous, and unforgivable, to see behind the Nazis' annihilation of six million Jews an "ultimate" motive to strike at Christianity! Was an effort to eliminate Judaism from the world not a complete crime in itself?

I repeat, the Pope is a Roman Catholic, and therefore by definition believes that the Church is the true religion, established by God Himself. Other religions, which reject essential Christian teachings such as the divinity of Jesus, are false, and of necessity less important in the greater scheme of things than the True Faith. It is hardly surprising for someone who believes this to regard Judaism's main function in history as having brought forth Xianity. Seen through a Xian lens, which is the only lens he's got, the most important aspect of the Holocaust must be the implied attack on Xianity. As for the elimination of Judaism from the world, like every Xian, the Pope surely wishes for such an event – if all Jews accept the the truth of Xianity and convert, then there will be no more Jews, and from a Xian point of view that must seem like it would be a very good thing rather than a bad one.

Muller goes on to attack the Pope for singling out St Edith Stein, and saying that "she accepted death with her people and for them".

the face he sees is the face of a person who left Judaism behind to become a Catholic. So many Jewish authors, actors, scientists, lawyers, doctors, politicians, artists, and musicians were murdered there. And so many rabbis. And yet the face that makes the horror real to Josef Ratzinger is the face of a Jew who converted to Catholicism, and who died not only "with" the Jews, but somehow also "for" them. What does this mean, her dying "for" the Jewish victims of Auschwitz? Apparently when the death camp worker dropped in the Zyklon-B, and the Jews in the gas chamber began to asphyxiate, somehow Edith Stein died a more consequential death, a death not just "with" the others in that room, but "for" them.

Again, to a Catholic this must be not only unobjectionable, but the only possible way to see things. Edith Stein is a martyr and saint of the Roman Church; of course her death is more significant to a Catholic than those of others. And it is (I understand) an essential RC belief that saints can die for others, and can redeem others' sins, as Xians believe Jesus to have done for all humanity. (Any RCs reading this, please correct me if I've misunderstood.)

So it seems to me that Eric Muller's complaint boils down to the very fact that the Pope is a Christian, and a Catholic. I wonder, is he as offended by the toilet habits of bears?