Rufus
I wondered that myself. Certainly I can quote the Bible and tell you the tenets of my beliefs, but I don't belong to a particular denomination or church. The church I was raised in didn't keep records of baptisms since it's not considered a 'rite' for membership like Catholic or CoE. TBH, many protestant churches don't keep records of baptisms as they're simply considered public professions of faith, so one would really have no way to 'prove' they were a Christian based on a paper trail.
So it does make you wonder. Are they going to ask them to quote the Bible? Explain the Trinity? I expect any 'terrorist' would be taught to memorize these things, just as many Jews were saved by being taught the Catechism in WWII.
And what about other 'non-terrorist' (those are 'finger quotes' btw) religions. What if you are a Hindu, a Jew, a Zoroastrian, or an atheist? Are they being stopped at the borders, too?