Maybe because I am pagan I do not think my religion is the one true religion. Technically I don't even believe in Norse gods. I hold gods as incarnations of desirable human characteristics not actual beings. Something started creation and that something may be god but to say your's is the one true religion is a bit much. The article mentions orthodox and protestant faiths but does not mention the Jewish or Islamic faiths. A bit snotty and snobbish to look down your nose at others and scoff that they are not the one true religion of Jesus Christ. What about a one true religion of NOT jesus Christ? Who would that be?
Well, to get technical about what the article discusses, even I took it out of context. It doesn't discuss the church being the true religion, but rather, the true church (as in, "we're the best Christians, so there"). And it nitpicks to define what other christian sects should be called. I don't think the term 'church' applies to the jews or the islamists does it? mosques, synagogues, masses, religion, yes these terms apply. But I've never heard a Jewish person apply the term 'church' to their religion.