Did you ever do one of those volcanoes in grade school, with the vinegar and baking soda with food color in it? The vinegar and baking soda together in the cake have the same chemical reaction during the baking, and gift it lift and make it nice and light and airy.

If there's a bit of tanginess in the cake, it's hidden well under chocolate and sugar, and probably comes from the buttermilk, not the vinegar.