He's insane. His religion is insignificant even tho the OP is trying to equate Christianity with radical Islam.
This is an all too familiar practice for these unintelligent apologists for Islam. Their big 3 techniques seem to be these:
1 -- Matter or prevalence. They find something like this which is extremely rare in Christianity to compare to something quite common in Islam, inevitably using an example of something routinely condemned by Christians and fairly widely supported by Muslims.
2 -- Matter of magnitude. They find something mildly annoying in Christianity to compare to something really vile in Islam -- I/E Christians shunning those who leave the faith as a comparison to Muslims killing apostates.
3 -- Matter of time. They find something in Christianity's past to compare to the Islamic present -- Spanish inquisition or witchcraft trials. It's as if the world has experience some weird rift in the time/space continuum.
All degrees, and all irrelevant Probability Fallacies.
The question is not, "is it true (or likely) that Islam/Christianism/whatever religion is the root cause of this (beheading/terrorism/violence) incident?"
-- Rather, the question is, "does the fact that the perpetrator of this event is a Muslim(/Christian/Jew etc) tell us that such an act is a Muslim (Chrisitan/Jewish/etc) act?"
And the answer to that question
must be consistent, regardless which religion or which event is plugged in. The answer
must always be the same.
And the answer is "no". It
cannot vacillate between "yes" when it's "them" and "no" when it's "us".