The terms were interchangeable back in the Cold War, everywhere outside academia; and there are interesting continuities between the Tsars and the Soviets. "Glasnost" and "perestroika" were first used in reference to Peter the Great's policies, and Great Russia (Russia proper) was known as Red Russia as far back as, I think, the 1400s.
Also: _The Structures of Everyday Life_ and _Simplicius Simplicissimus_ both touch on Russia, in ways that suggest that the country (post-Mongol-conquest) always did have a certain amount of proto-Sovietness to it -- alcohol sales as a state monopoly, for example, or arms always coming from royal treasuries.
It was used during the Cold War, because it was important to simplify, demonize the enemy. Russian Ivan with bottle of vodka, in a tank, driven by a brown bear with ushanka creates an a lot more simple image; you add Ukrainians, Kazakhs, Armenians, dozen of languages, without profound racial discrimination - and people will start having the Thoughts; counterproductive for the narrative of the Cold War.
Communist Russia was coming apart at the seams, and it took the US many years to realize it. There's a lot of complexity.