Russia isn’t really a Christian nation, it merely has a government ceremonial church with formal cultural ceremonies like marriages and suppresses actual practicing and believing Christians who don’t belong to it.
From your source that you posted.
“Another criterion to count religious populations in Russia is that of “religious observance”. Based on this principle, very few Russians would be religious. It has been found that between 0.5% and 2% of people in big cities attend Easter services, and overall just between 2% and 10% of the total population (3 to 15 million people) are actively practicing Orthodox Christians.”