Show me where the post you replied to actually claims that Finland, specifically, was under the rule of Stalin.
Look, you're absolutely correct that Finland resisted the Soviet invasion and was ultimately successful in doing so, and at worst very few Finns were ever under Soviet rule and only for a very short time. Nevertheless, it's not worth giving Holocaust deniers and neo-Nazis even the smallest bone to gnaw on, because you know they'll go back to their friends and say, "You know, those pseudo-skeptics wouldn't even admit that Stalin invaded Finland." The USSR invaded, among other countries, Finland; the USSR placed millions of people from other countries, albeit not the Finns, under Stalinist rule. Both of those statements are true; it seems the only thing you're objecting to is them being put next to each other.
Dave