"Hili ni tunda" is best translated as "This is a fruit", so this answer certainly should be accepted. Translating in the other direction "This is fruit" is best translated as "Haya ni matunda," due to the nature of the noun "fruit" in English. It is almost like milk (but not quite); anyway, in that case, one would say "Haya ni maziwa." ("This is milk")
I see what you mean, but surely because of the nature of the noun 'fruit' in English we would say, 'This is an apple', 'This is a pear', etc, or possibly 'This is a piece of fruit'? I suppose if one were teaching primary children one could say, 'This is a fruit, [but] that is a vegetable,' ….