Although this is hypocritical, I think it was mainly the sentiment behind the comments and implications. The guy who said Christianity was mainly referring to general ideals and values which are shared by most christians, whereas the guy who said islam might have been alluding to certain events which don't represent the religion as a whole. I think for most people, Islamophobia is just a touchy subject, meanwhile you dont see people saying that they're scared christians might have a bomb. The worst you'll hear is that most christians are homophobic or something. And also christian people generally seem to be more fanatical than other religions. I think the fact that more people have encountered christians/cristians are more loud might also tie into it