I don't really know much about the grammar, but it is regarded as a question as it is asked in a questioning tone. Basically, it's pretty much the same as the English conversation you found in movies and books.
For example, "You eat oranges?" It has a same meaning as "Do you eat oranges?", but for English, that would be grammatically incorrect.
I don't know if Indonesia has the same grammar structure though. But, it is safe to use in a conversation.
Agree there are times when the "correct answer" is inconsistent. I am annoyed that ada is not accepted for punya. Everywhere I've been in Indonesia uses ada when maybe punya is correct. I think the problem with duolingo (and mostly I like it) is that it is being too grammatically rigid and not reflecting current useage. Don't get me started on Musim Gugur - Autumn/Fall - they DON'T have autumn or spring or winter it's hot season, dry season, rainy season