Wine production was originally established in Tanzania in Dodoma Region by missionaries - supported by the former President Nyerere according to this website (which may only answer some of your questions about wine in Tanzania).
I have known of Tanzanian wine ever since a friend of mine, who stayed with me for a while in Dar es Salaam some years back, decided to follow his conscience and buy Tanzanian.
We eventually had to give up drinking it, though we tried hard. It wasn't good, and it only fed my disbelief in the whole idea of wine from Tanzania.
Tanzania, and East Africa, has little tradition for wine-drinking - and for growing and producing wine.
But never say never. This is what I love about this place - just as you concluded 'no' - the opposite proves. Yesterday, I visited Cetawico ltd - wine producing factory in Dodoma Region (- and later during the afternoon someone treated me to several glasses of the Presidential in the outstanding Italian Sipe Cafeteria in Dodoma).
Wine is not an easy business. It demands investment, the right kind of soil, plus rain and sun in adequate portions. Too much rain and too little sun may destroy a whole harvest.
It takes people to grow, nurture and harvest the grapes - and for a small-scale farmer it is also an investment in the sense that he relies on the outputs from two annual harvests. The farmer shold also understand that people in the receiving end expect a certain quality. Like with coffee. Grapes or coffee beans are sophisticated in the sense that quality in regards of i.e. flavour is fundamental. Wine isn't just wine - which to some extent actually also could be said about many other crops, but the point in this case is that Tanzanian farmers may not have extensive experience with the output of the grape production as they may have with other crops.
I can recommend you shop Tanzanian next time. The Cetewico wine is for sale in Dodoma and in Dar es Salaam in Srijees in Oysterbay and Shoppers' Plaza.