I'd love to know how a tomato became nyanya.
Fact. In Kenya we call our grandmothers nyanya. :) In Tanz. they call them bibi. Which is funny because bibi in Kenya means wife. Lol!
So you call your grandmothers tomatoes, and they call their grandmothers "wife". I'm not sure which country's grandmothers get the better deal. ;)
Or, maybe, do you mean how a nyanya became a tomato?
In Zanzibar Portuguese word is used for tomato: tungule