What exactly is a "short chair" supposed to be? Especially as opposed to a small chair?
Definitely a bad translation. Chairs are small, not short. Report it!
'Kiti' can also be used for stool which is the earliest form of seat furniture. So in that sense you can say, a short stool which makes sense.
Duolingo should add stool as another meaning for Kiti to get that idea across.
Chairs are not referred to as short, even if they are so. They can be low-backed or high-backed. A highchair means something else, of course. They can be large or small. I don't think that a short-backed chair is necessarily a small chair.
Maybe a low chair?
Small chair not short chair in English
When translating to English, are articles optional or mandatory?
Optional, since there are none in Swahili
except "short chair" is rejected here...
That would be another article-related error by Duolingo Swahili
Come on people! No-one says a a short chair
There are no short chairs, only small ones!