It’s pointing out that the countries like Estonia, Ukraine, Finland, etc were genuine collaborationists with the Nazis, or had sizable pro-Nazi factions, like the OUN in Ukraine, yet the non-aggression pact between the Soviets and Nazis is framed as an alliance, when the Soviets spent the last decade trying and failing to get the west to form an anti-Nazi alliance, so the Soviets made the same kind of pact the west had already made so as to buy time for development for the coming war.