I have had a very dark beer described as a chocolate stout, not because it contains or tastes like chocolate, but because of the color. On the website for Highland Brewery, the description states that their “Black Mocha Stout” derives its chocolate and coffee tones from the use of appropriate roasted malt grains…
The term “chocolate stout” is similar to the coffee term “mocha”. In many instances the term is used to describe a variety of “caffè mocha’; but the term “mocha” actually refers to a type of arabica coffee available only from Yemen. I attended a coffee-tasting in 1979 or 1980 where a coffee from these beans was featured. There were some chocolate notes in the nose, and some lingering in the after-taste, but there was no chocolate used in either the roasting or the brew.