@TomSea
Somehow I think they are ignoring the Muslim Turkish population,and focusing on the Christian Turks.
"Christian Turk" is a nearly non-existent category. Christian citizens of the Turkish Republic are pretty much all Greeks, Armenians or Arabs (the original seat of the Patriarchate of Antioch is now in Turkey, though the primary cathedral and partriarchal residence have been in Damascus since the Mamaluke era). Ethnic Turks are pretty much all either Muslims or secularists, and have been since before the overran the Empire. Okay there are a few notable counter-examples (St. Ahmed the Calligrapher, a court official of the Ottoman Sultan who secretly converted to Christianity and was martyred in 1682 when his conversion became known, and St. Constantine Hagarit, another convert martyred in 1819), but not enough of them to make a difference in demographic calculations.
Ataturk's secularism got a lot of Turkish Muslims to be fairly secular and Western in cultural attitudes, and thus, lowered the birthrate, esp. in urban Turkey, something Erdogan is trying to reverse, but the Kurds in eastern Anatolia still have the Muslim (or really pre-modern) attitude toward childbearing/rearing and have larger families, hence the article's analysis of Turkey's demographic future.