This Brandy Cocktail recipe is just one variation of the classic drink. The drink is the formula for the original definition of a cocktail: distilled spirit, sugar, water, bitters. In the early days of cocktails (late 1800's) you would order a basic 'cocktail' by calling the base spirit such as a Gin Cocktail or a Whiskey Cocktail, or almost any liquor of choice and it would be made similar to this. In the case of this recipe, the curacao liqueur acts as the 'sugar.'
If you want a "Fancy Cocktail" you would typically get one garnished with a lemon, again with your spirit of choice (technically making this recipe a "Fancy Brandy Cocktail"). How simple those days were.