I don't know if the two were Christians either. If they weren't, their conduct wouldn't surprise anybody.
But anybody who professed to be a Christian? Whole other story.
Mt 10:33 But whosoever shall deny me before men, him will I also deny before my Father which is in heaven.
I am a professing Christian. But if I were in a scenario where an Islamic thug was threatening to kill me if I didn't renounce Jesus Christ and worship Allah, I have to confess, I would probably resist not because I am guaranteed eternity because of the truth of the Gospel and the promises of God, the highest and noble expression of that resistance.
I'd do it just to PO the thugs.
That's just me, though.
It's a hell of a challenge... not to be taken lightly. I find it quite telling that the DBM never even considered the story from this perspective.