You are wildly incorrect. The Winter War ended well before the Continuation War began. See: The Treaty of Moscow. And it was not just a few German troops. Finland served as a staging point for a major if unsuccessful assault on Murmansk. More important, the Finnish invasion (and taking of Karelia) helped tie down Soviet forces near Leningrad. The alliance was eagerly sought by Finnish politicians convinced (not unreasonably) the Soviets would attack after many months of belligerence toward the Finnish ambassador by Molotov. But they were also convinced that Germany would inevitably defeat USSR and usher in a New Europe (code for fascist Europe - long racist toward Russians, the Finns relished the fraternal ties to Germany and the privileged place they could assume in this new world order).

Finnish leaders actually served time in prison after the war for their war crimes. I am sympathetic to Finlands position but to say the Winter War never ended is an absurd falsehood. An entire book was written about the period between the wars by AF Upton. Finland In Crisis. It is superb. It details extensive deliberate planning at the highest levels between Finland and Germany for months prior to Germany turning on its then ally USSR.

(Here’s a quiz for you. If it was only a few German troops in Finland who quickly left, why is it they burned so much of the north and center of the country e.g. Rovaneimi on their way out and why did Finland have to fight them to get them to leave? They were dug in in bases supplied by Finland.)