Hi, mawoods, welcome. Well--if you look at potable, which means fit to drink; drinkable (from phrontistery), the connection may be a little clearer. (Um--potable is also used as a noun, sometimes, as in the Jeopardy category Potent Potables, usually referring to alcoholic beverages.)
The quote from the W.A.D. def., "An expert's guide to the potatory pleasures of port, sherry, montilla, and madeira.", means that the drinking of port, sherry, montilla, and madeira is pleasurable.