This goes very far back. Before Rome became the official seat of Christendom, there were several contenders that claimed to be the center of Christianity. After Rome fell, and the Roman Empire shifted its seat to Constantinople (now Istanbul), it became the new center of Christianity.
When Constantinople fell in 1453, the Russians assumed that Moscow was to be the new center of Christianity. However, this didn’t happen, and the center switched back to Rome.
And the Russians have been peeved about this since.
Putin revitalized the idea, in a masterstroke, inviting the heads of all the Orthodox Christian churches but the Roman church to come to Moscow for a conclave. And that has got the ball rolling to the idea of Moscow being “the new Rome”.
So I am not surprised at all with the idea that Russia is the only major nation not “enslaved” to socialism or other anti-Christian rule.
It’s more a question of the center of Orthodox Christianity. From the Orthodox POV, Old Rome fell into schism and heresy over time and the primacy devolved to Constantinople per the canons of the Ecumenical Councils. With the fall of the Roman Empire in 1453 Russia became the largest Orthodox land not under hostile occupation by either the Turks or Catholics. Thus the myth of the Third Rome was born.
I think it is a bunch of baloney, but all countries have their nationalist mythologies. That said, the good father really needs to be reminded that Phyletism is a condemned heresy.