Poland was responsible for the outbreak of WWII the same way Archduke Ferdinand was responsible for the outbreak for WWI...
Directly it wasn’t responsible at all. Nor did Soviet Union.
Germany and Japan are responsible.
But then if you are somehow creative and political in your reading of history you’d easily find the factoid to blame either Poland or Soviet Union.
Poland has it’s part of bull to smear and so does Putin.
Both are factually right but biased in their opinion.