Christian renegades were an important element in the constant wars between the Cross and crescent in the Mediterranean. Many possessed needed technical skills which aided the Moorish sea rovers in improving ship construction and cannon casting. This phenomenon seems to be returning.
Well, by definition they weren't Christians. You don't even need to go into the 'you will know them by their fruits' path. I suspect in these cases, as in the 'Director's son', they were brought up in a 'cultural Christian' environment - that is, celebrating Christmas and Easter, and attending church the perfunctory twice a year - but they never really believed.
Just like Great Britain might call itself a Christian nation - but that is just from its cultural heritage (Queen Victoria: 'Great Britain is great because of the Bible') but I suspect that the Christians in that land are probably in the sub-5%, or less range. Just living off the successes of a former people who really did believe and fear God. And 'Christian America' isn't much better. We're probably in the 20% range.
I'd just call them 'renegades' - or renegades and traitors to their Nations.