BY AZURA, BY AZURA, BY AZURA!!!!!!, he isnt right.
Thats what i was thinking. No way would something as important to the nords as Nord Mead not be made in Skyrim. Then theres all the farming going on which i assumed a bit of it was for creating wines. Also all the berries and such in the wilderness is a veritable gold mine of wine making resources. On top of the you got trading which from the looks of it still going on with the Empire since the war is with the Stormcloaks not Skyrim. Oh and lets not forget trading from other races and the black market.
Maybe the stromcloaks have a secret lab under skyrim that makes wine, and imports it to your local stores in skyrim.