I answered "...in Duolingo" and was given credit and told it was a typo, but I actually had a different meaning in mind. I was imagining that Pöllönen was the vihreä pöllö, rather than someone using the site/app. Would my meaning be expressed differently in Finnish, or is the sentence ambiguous?
That's a good point! Yes, if you translate the word in the beginning of the sentence as "little owl" rather than the name Pöllönen, it could be about Duo the owl. I'll add that as an alternative translation. It will take a week or two for the course to integrate my edit. :)
Originally -nen meant "of". That's why so many Finnish last names end in -nen: Virtanen ("of the stream"), Jokinen ("of the river"), Järvinen ("of the lake"), Pöllönen ("of the owl"). In modern Finnish -nen is indeed more likely to mark a diminutive. It doesn't always do that but it's still relatively common. For instance, kukkanen means "little flower" and, yes, pöllönen is "little owl". :)