I have no idea what he could have said. I know what he said "シテ~?" That if you translate that word you get "Shite ~?" And what it means in Finnish I have no idea, maybe it's not Finnish at all, but even in Japanese I couldn't find any explanation.
Скорее всего автор просто восхищался Финляндией (или знакомые там есть) и решил её использовать в манге, не зная, какие они речевые обороты на самом деле используют.
I know about this problem. I live all my life in Russia and I have no experience in spoken English, only written and because of this it is uncomfortable for many people to read this, but I don't know people who can help me, so if you want to help me (on a voluntary basis as I don't have money...