I don't think they decided that, they included Finish which is completely unrelated to the other nordic languages. If they just picked languages that are related for cross learning including Dutch or German would have made more sense indeed.

The company is based in Finland, they started with Finnish

I understand, not saying they did something wrong just pointing out the selection of languages was not because of them belonging to the same family but rather to serve a certain region.

The root is unrelated but Finnish has certainly been shaped by Swedish and Russian and most recently English languages in the last 200 years

Including Finnish was probably just a political choice, since Finland and Sweden are very close politically, much closer than Germany or other areas with more similar languages.

This was done by a Finnish company and university. They would've included Finnish even without any political motivation.

The nordic languages are germanic except for finnish, but yeah finnish is an exception and I'd expect most small LLMs to struggle with it.