At least the wikipedia articles seems to agree with the author.
These cities continued to be used by the Christian natives
as protection from the Mongolian incursions of Timur in
the 14th century.[7][8]
After the region fell to the Ottomans, the cities were used
as refuges (Cappadocian Greek: καταφύγια) from the Turkish
Muslim rulers.[9] As late as the 20th century the locals,
called Cappadocian Greeks, were still using the underground
cities to escape periodic waves of Ottoman persecution.[9]
R. M. Dawkins, a Cambridge linguist who conducted research
on the Cappodocian Greek natives in the area from 1909-1911,
recorded that in 1909, "when the news came of the recent
massacres at Adana, a great part of the population at Axo took
refuge in these underground chambers, and for some nights did
not venture to sleep above ground."
