But if it taught you it as just rice, and then you got ninakula wali, would you then think wali and mchele were synonyms, or would you work out the distinction between cooked, edible rice, and uncooked?
There are probably better ways that they could have handled it, but some method of distinction is called for. Some sentences they don't distinguish, and people complain about that as well.
I think the way they should handle it is:
If they give us the sentence Ninahitaji mchele they should accept both "I need rice" and "I need uncooked rice."
If they give us Ninahitaji wali then both "I need rice" and "I need cooked rice" should be accepted.
If they give us the sentence "I need rice" they should accept both Ninahitaji wali and Ninahitaji mchele.
If they give us the sentence "I need uncooked rice" then only with mchele and "cooked rice" only with wali.
... because we're not mind-readers. If the English sentence is not specific, the Swahili translation should be any possible translation. If the Swahili translation is more specific, they also need to recognise that we do not have to be that specific in English and accept what we would probably actually say.
I find these weird expressions like "uncooked rice" are ok in multiple choice exercises, but when it requires us to translate sth by ourselves, it's really annoying when it forces us to use a specific wording (which is often wrong in English) in order to finally complete the damn exercise :-D Especially the lesson about times was really annoying. Instead of accepting "7:30" it wants you to write sometimes "seven thirty", sometimes "half past seven" etc