Moreover, if you go almost anywhere in Siberia, 50% or more of the locals will be of ethnic minorities native to the area (you may describe their appearance as Asian). More in rural areas. Many regions are dual language, Russian + indigenous. This includes the largest administrative region on Earth that is not a country.
They speak Russian, a Slavic language. The culture is clearly linked and descended from the Old Slavonic people.
I'd love to know about the thinking as I'm scratching my head here. This is the first I've heard this claim and I am half Finnish, quarter Russian by ethnicity. My grandparents certainly did not think they were from the same ethnic group.
Modern Russian is a little bit older than hundred years.
"Pre-reform" language was significantly different in script, vocabulary and grammar and wasn't older than hundred years itself. Before Napoleonic war 1812 nobility was speaking French, ruling family was German and serfs were speaking Polish, Belarusian, Ukrainian or one of the Turkic dialects.
The only slavic parts remaining in the modern Russian is Cyrillic script and words borrowed from Ukrainian.