We still haven't established if the claim is actually true or not.
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Wait.
There was a study recently that showed that theists can endure more pain.
Is it possible they extrapolated from there to torture?
It would really depend upon what we call "brainwashing." There once was a worry that a person could be put under severe stress which would allow an evil person to implant false memories which would later be accepted as fact. This sort of thing is in same category as stage hypnotists which can make a person cluck like a chicken when they hear a bell.
Since I haven't seen any more of this than is in this thread, I'll speculate that someone has claimed that Christian POW's resisted interrogation and refused to cooperate for longer than less devout POW's. The Christian church has a long tradition of martyrs who suffered torture and murder and remained faithful till the end. Beyond that, prayer is a powerful distraction while your arms are being pulled out of their sockets.
Whether this is true or not, it's not difficult to imagine such a thing, even if it is difficult for an atheist to imagine a situation where a devout person would have an advantage.