I would have thought Europe’s Christian population was much more than 66% in 1910. There were Muslim majorities in Turkey-in-Europe and Albania and significant numbers of Muslims in Bosnia, Kosovo, Bulgaria and a few other places, plus some districts of the Russian Empire. Add the Jews and any freethinkers and I doubt they add up to 34%.
Blogger seems to be making stuff up.
Pew from a decade ago found Europe over 70% nominally Christian.
https://www.pewresearch.org/religion/2015/04/02/europe/