I'm not surprised that Atheists, Jews, and Mormons did the best on this. Most everyone will know your standard Catholic answers, and progressively fewer people will know about reformation, religious rights, and alternate world religions. Minority religious groups are more likely to know the questions about their minority religion, but still know the "basic" questions about Christianity and religious rights. Atheists have often done a "religious walkabout" and have some bare-bones knowledge of most world religions. In my experience, they also care about religion in government more than religious people. Basically, it seems like this test was designed to produce the results it did. I don't think you find any meaningful facts from the performance of different religious groups.