I do not know if it is completely wrong in its other aspects, but Finland has never been communist nor socialist country. Yugoslavia was a socialist state, but outside Warsaw pact. Misunderstanding by the map makers might come from mistaking treaties with Soviet Union to be an indicator of political/economical systems.
Finland made a treaty of friendsip, co-operation and assistance with Soviet Union in 1948, which stated that Finland would prevent any attacks from Germany or its allies through Finland against USSR, and Soviets would help in that. Unlike treaties made between Soviets and other Eastern European nations, this treaty stated that both nations needed to agree there to be a german threat for it to be activated, which it never was, despite some Soviet attempts. Stalin said of the treaty when signing it that it was Paasikivis, the Finnish president, dictate, since Finns had only agreed to the deal with a clause that military consultations would need both nations to think there to be a threat. This difference between treaties might be invicible to casual observer, who just sees the translated name of the treaty and sees it to be the same as with all Soviet client states in the Eastern Europe, while the treaty itself was different.
Yugoslavia on the other hand was a socialist country, but they were at odds with USSR. They even received military aid from US to help them to remain outside of Stalins influence. So in conclusion I believe the authors of the map used treaties with Soviet Union as a proxy for economic/political system, which lead them into making errors in the case of Yugoslavia and Finland.
Postscript. Finnish warplans were made in secrecy during the Cold War, and the real ones always presumed USSR to be the enemy, despite any treaty oblications. Fake warplans were made to be shown to politicians, some whom were known to leak information to Moscow. In these plans attack came from anywhere except East.
It may be important to create a distinction between the Soviet Bloc and the Communist states. Communist states were not always in the Soviet sphere of influence. Vietnam and North Korea were both Communist states but were more aligned towards China than the Soviet Union. Its a misconception and misunderstanding of Cold War politics to say that it was purely a USA vs USSR conflict. While both powers developed spheres of influence over less powerful nations and funded proxy wars and conflicts abroad, it wasn't the only conflict.
Tito was the leader of Yugoslavia for effectively most of the Cold War, and he was a resistance fighter against German occupation of Yugoslavia during WW2. Tito and his government were very resistance to submitting to Stalin, who had the goal of cementing Soviet influence over Eastern Europe. The establishment of the Warsaw Pact and Cominform, as well as later attempts to assert pressure through incidents such as the Berlin Airlift would show this.
Tito was very anti-Stalinist, but much like North Korea, Vietnam, and China at the time, although they didn't submit entirely to Soviet influence, they were still Socialist regardless. Tito largely had a falling out with Stalin due to this hard clash between their personalities and methods of diplomacy. Tito acted outside the will of Moscow, largely in the Balkans where Tito established independent relations with other Balkan nations, including making plans with Bulgaria which were never formalized, to create a Balkan Federation of Socialist states as a bloc of power counter to the Soviets.
Yugoslavia was expelled from Soviet aid and organizations and was repeatedly pressured throughout the Cold War by the Soviets, including multiple assassination attempts on Tito. Yugoslavia would become one of the core founding members of the Non-Aligned Movement, a major international political movement opposed to the Cold War entirely.
Yugoslavia was without a doubt a socialist nation but was outside the typical spheres of influence that was established regarding the ideologies in the Cold War.
As for Finland, thats a rather curious case. Finland did have a lot of socialist/communist influence throughout the war, but a socialist government was never formed. Only in the late Cold War did a left-leaning party take the presidency, but they weren't socialists, they were centre-left and still capitalists. The Socialist party in Finland did see success, even narrowly winning the most seats in the 1958 parliament. But that didn't secure them a majority of seats nor did it give them total influence over the nation. Although they joined several governments, and at one point had a Prime Minister between 1946-1948, they never formed a socialist government.
I find it highly unlikely that Finland could be considered communist or socialist. Although the presence of leftist political parties was large and they did secure positions in the government from time to time, Finland was never a socialist nation.