"a good friend"
I'm going to explain this but bear in mind that Duolingo is not using this logic because on many occasions they are using the wrong words.
The word جيد simply means (good).
The word طيب is used in various contexts. It can mean "kind" (i.e. nice) as well as "delicious".
However, there are more accurate words for "delicious" that I think Duolingo should have used in sentences related to food, like شهي (šahiy) and لذيذ (laðíð) - and the latter one is quite common.