Ask Lemmygrad

If you say this to the Finnish, they will get visibly incandescent.

Finland was part of the Russian empire so there are some Slavic influences on Finnish culture, but there are probably even more Swedish influences since it was also part of the Swedish empire at one point. Linguistically it's neither Slavic nor Germanic.

both major nationalities of finland, the finnish and sámi peoples, are speakers of finno-ugric languages, a branch of the non-indo-european uralic family. finnish swedes speak swedish, a language in the germanic branch of the indo-european family. slavic languages are spoken predominantly by immigrant communities, the largest of which is the russian-language community, consisting of about 1% of the population.

Novgorod and Sweden had a race to conquer sweden back then. A lot of finnish tribes converted to orthodoxy before the swedish conquest. The russian ethnogenesis also included significant finnic components.

But no finns aren’t slavs.

Well you have Sami people who are indigenous to the northern lands and white Finnish people who at best can be grouped in with the Baltics. Definitely not Slavic.

No

Lmao, what? There are more reasons to consider Russia Finnic instead (very little and very flimsy reasons).

No. Hope that helps :)

His reasoning was that Russia and Finland share a long border and a lot of history

Sharing a border is no condition. Austria and Hungary where once a state, however Hungarians are not Germanic (The stuff about Austrian identity, Austrians as ethnic group and so on is actually rather new and I am way not an expert). Funny enough both differ in the language the same way as Finland and Russia.

no, its not.

In terms of genealogy the Finns are most closely related to neighboring Finnic groups Estonians and Sámi, not Russians specifically, East Slavs in general, or any other Slavic population.

In terms of culture Finnish culture is largely indigenous with a mixed of a larger Swedish influence and much smaller Russian influence but are still culturally Finnic in most respects.

In terms of language the Finns speak a Finno-Ugric language like neighboring Estonians and Sámi, not a Slavic language like Russian or anything else.

Politically speaking Finland has long gravitated toward Scandinavia and thus the West and less so Russia or other Slavic countries even when it was part of the Russian Empire.

Religiously Finns are mostly Lutherans, itself an import from Sweden, and there is little Orthodox presence to tie them to Russia's own religious history. They also have an indigenous religion that is very clearly Finnic, not Slavic, in its customs.

So in every possible way that could matter: no, Finland isn't Slavic regardless of how the word is being used.