Not just technically true, but the reality for vast areas such as the Ukraine and Kazakhstan etc which existed even then. There were numerous cities such as Vilnius or Dushanbe where most of the population did not speak Russian as a first or even native language or consider themselves Russian. It's like when people watch/read "Hunt for Red October" and call Captain Ramius a Russian... He isn't one, and it's a pretty key plot point that he isn't one, hence he defects.