Translation:The strange Australian man does not know how to barbecue properly.
This has several problems:
"does not know how to" = "cannot", "can't"
"barbeque" = "grill"
"properly" = "correctly"
I said "...cannot grill correctly" instead of "...does not know how to barbeque properly", and it was marked wrong even though the English has exactly the same meaning.
It is frustrating to have to coach the course through all the permutations of word usage, but it seems that's just how Duolingo works. The other night I got the same question "wrong" ten or twelve times in a row, on purpose, so that I could enter and report every combination of words that were wrongly marked incorrect!
Unlike many other languages, Finnish doesn't have a rising intonation in questions. And in general, intonation plays a smaller role.
As for the computerized speech, it's just a computer. Real speech is of course more varied, but grammatically the flatter speech would also be acceptable in Finnish.