Even if USSR didn’t occupy Poland for 50+ years,they “Liberated” Poland for self interest reasons not altruistic ones.
Screw ‘em.
And they ‘moved Poland over’. If you look at a map of pre-WWII Poland and post war Poland, you’ll see that Poland somehow moved west. Essentially the Soviet Union kept the part of Poland they gained in the Hitler-Stalin pact which was what Russia lost in the Treaty of Versailles. In compensation, the Soviets “gave” Poland some of Germany.