One of my Christian friends told me that as she was taught in Catholic school, any other division of Christianity was to be considered a cult, regardless of the fact that it was still a form of Christianity. Now, she doesn't personally agree with this, but this was the way it was taught to her in Catholic school when she was a girl (about twenty years ago, give or take). So, to whatever "branch" of Catholicism her school praticed, other churches such as United, Baptist or Presbyterian, are all to be considered cults and don't practice the "right" form of Christianity. I've heard other Christians say similar things (it usually spawns from a discussion about what I consider cults, like the followers of David Koresh or Charles Manson, and then turns into a conversation about what they were told, in school, were cults, and how the definition varies), so the pope's comments don't seem completely out of place to me. I don't agree with them, but I can see where the mentality comes from -- that everyone else is wrong but him and those who agree with him.
It is not a mentality that is likely to foster religious peace and unity, that's for certain.