Surveys like this are always of “self-identified” Catholics, which can mean they’re deeply involved in their faith, or it can mean they were Baptized Catholic, but have zero active participation in the Faith, and even hold anti-Catholic/heretical beliefs.
Therefore, it’s not exactly a true reflection of Faith. When it comes to Evangelicals, their Faith is self-affirmative. That is, because they reject infant Baptism, you therefore have to be an adult to be Baptized Evangelical. This means that most Evangelicals are actively involved in their Faith because they made the adult decision to join it.
This is why their statistics are so high compared to Catholics, who may or may not be actively involved in their Faith because not all Catholics actually make the adult decision to participate in it, yet they still identify as Catholic because their parents Baptized them as such. These non-engaged Catholics are what you might call “lukewarm,” who don’t really care one way or the other about deep religiosity, and think about it superficially.
It should also not be surprising that Athiests scored high as well. Unlike the younger generation of athiests, most adult athiests are post-Christian, and as such usually have deep-seated emotional angsts against Christianity. These people have a strong stance on deep religiosity, but one of disfavor (as compared to the favored deep religiosity of, say, Evangelicals), and so are generally familiar with major aspects of not just Christianity, but many other religions.
If you were to take a similar poll, and distinguished “engaged Catholics” from “disengaged Catholics,” the results would be strikingly different. As evidenced my members of this forum, who are certainly “engaged,” the knowledge is quite high, while you would almost certainly find the knowledge of disengaged Catholics to be strikingly low.
Great catch!