The use of "yang" would lead me to suggest that the more direct translation is "I pull the scarf which is red".
"I pull the red scarf" is obviously correct too, and perhaps slightly more natural for most situations, but I would think in this case the more direct translation should be accepted too. (I've reported it)
There's no special meaning to pulling a scarf. It's literally just exactly what it sounds like - pulling (moving towards you) a scarf (the thing you put round your neck).
Maybe there's a few different colours of scarves tangled up together, and you pull on one to untangle it.
Other than that, it's a pretty random thing to say.
This particular course is still in Beta, so it shouldn't be surprising that it's a bit unpolished in places. There's plenty of places where you'll need to use the Report button to get an valid answer added to the database, especially if it's a slightly more uncommon translation.
A lot of the other courses on Duo are much better, although I'd certainly agree that it should be treated as practice and not a dictionary.
In Facebook Indonesian, i got a notification that X Y menerima "friend request" Anda. They didn't use mendapat It seems that mendapat is just when you happen to have something given to you. But when you accept it formally and it's given to you it's menerima. ^non-native non-expert hunch. Someone please confirm the above.