Nobody claims they all speak Finnish well, but the Swedish spoken in Finland is influenced by Finnish and typically includes some loans from Finnish.

The person I was answering to literally claims people are bilingual (Swedish + Finnish).

Being bilingual is a fuzzy concept: to many, it includes people who speak a language less well, but perhaps enough to get by.

For example, in a bilingual environment, it can be enough to understand two languages and to speak one.

I have never heard someone say "I am bilingual" when what they meant is "I studied another language in school and can somehow understand a few sentences". To me, and I believe, to most people, being bilingual means speaking two languages fluently.

Personally, I'd only call native-level speakers bilingual, but this has caused misunderstandings.