That seemed really easy (32/32). The only questions a reasonably well-educated American might not know would be Maimonides, Jonathan Edwards if you didn't pay attention in US History, and maybe the one about which Christian sect believes in salvation through faith alone, if you were not a Christian and therefore uninterested in the theological differences between competing sects. Even that one was pretty easily guessable if you have ever encountered an Evangelical Christian trash-talking Catholicism.
I don't know the details of the original study, but the quiz was certainly very Christian-centric. It was more of a quiz about American religion for American Christians, asking only a couple of questions about essential aspects of non-Christian religions, while asking a bit more specific questions about Christian sects and of course throwing in a lot of US law regarding religion. This is interesting considering Christians had the lowest scores on the quiz.
I thought this was going to be a little more challenging regarding "unfamiliar" religions when I saw that Americans only got half the questions right on average. After taking the quiz, I find that statistic baffling. I don't think it really says much about religious groups so much as the sorry state of education in America.