It’s a bold and unsubstantiated claim. In English language there’s a lot of confusion because the same word Russian is used both for citizenship and ethnicity,

It’s a bold and unsubstantiated claim. In English language there’s a lot of confusion because the same word Russian is used both for citizenship and ethnicity, but in Russian they are different and such confusion doesn’t exist. If you run polls in Russia, ethnic minorities won’t say that they are Russians using the word for ethnicity, but they will certainly confirm that they are Russian citizens belonging to the same cultural space (and in that sense some may even use the word for ethnicity, e.g. “I’m Tatar, but I’m Russian too”). Nation is defined not by the government but by shared history and culture and may cross ethnic boundaries. Russia is big, but its people have developed the shared culture, the pride, the sense of belonging which qualify it for a nation. This comes on top of all geographical and ethnic identities, which make the picture more diverse and complex, but those identities are rarely stronger (even in regions like Chechnya).