I think the author isn't right saying that. The Russian word for solitude is уединённость, from word единый, that means united, integrated. That is a single whole, which unites many parts. That does bear a resemblance to what the author said, but a weak one. Moreover (I'm not completely sure of this, but almost completely sure) In old Russian language the word единый also imported single, sole. It's really very unfortunately that the author didn't explain his train of thought. Maybe there are facts I don't know.
Sorry for my English.