I would assume the source that says Jiana is of "Hebrew origin" has taken the attitude that the language of the ultimate start of the name is what should be listed, since
Gianna is an Italian feminine form of
John, which does ultimately go back to Hebrew.
I can't find an African origin for Jiana on short notice, and I am always suspicious of the claim that a name is "African" when the particular language or culture of
Africa the name comes from is not mentioned. It seems to me that someone who really knows what they are talking about should be able to trace the origin back to a particular culture or country instead of to an entire continent.