Don't mean to assume, but I'm guessing you're American?

The Nazis invaded in 1939. In 1938 the USSR was rapidly preparing for their invasion, which included detecting and rooting out fifth columns or just generally corrupt members of government who would hinder resistance against the nazi invasion. The idea that someone in 1938 would just be some innocent naive victim of crazy commie paranoia is ridiculous, since the nazis were literally trying to push for fifth columnists to cause disarray in the USSR at the time and the USSR was in a desperate race to secure their defenses against the Nazis.

Additionally, with regards to Poland, the western description is usually "evil commies invaded Poland because they're evil and best buds with the Nazis" but in reality, the USSR only went into Poland after their government collapsed and fled, and the Polish government's last decree was to not resist the Soviets. In turn, the territory claimed by the Soviets was itself stolen from the USSR in their earliest days by Poland in an invasion directly after the Russian civil war, when the newly formed USSR wasn't in a position to defend itself.