Translation:Strange! He does not want to drink coffee, although he is Finnish.
To my understanding, partitive can be used as a measurement for definite and indefinite amounts of something, as well as with abstract ideas/negative sentences. Regarding "outoa," what it describes here is the finnish person not wanting to drink coffee.
No coffee drinking is taking place. Rather than assuming Finns drink coffee at all times, you would expect they have already drank some or haven't had any yet. But we can infer from context, s/he turned down an offer (haluatko kahvia?), and the person who asked was surprised. The idea is both abstract and negative, therefore written in the partitive case.
OUTRAGE! Can such be possible? Next they'll say they don't like saunas! I live in Norway and refuse to ski (I'm not Norwegian). This is heresy, but after saying this in front of the locals, you'd be surprised how many Norwegians will quietly admit to me in private that they hate skiing too.
"although" is the opposite of "even though". I think the correct translation is "even though". When you say, "even though" you are offering the fact as a point that gives rationale for the strangeness, whereas "although" serves to mitigate the strangeness.
In other words,
even though = "he doesn't like coffee, despite of the fact that he is a finn and they all love coffee"
although = "he doesn't like coffee, but that makes sense, he's a finn, and they don't like coffee"