Caloric density isn't complete bunk. There are definitely uses for high-calorie low-weight foods when it comes to activities like backpacking in the wilderness. No one wants to lug a ton of food around if they can get similar calories while carrying less. With what I'm getting from the quote, it seems like they're trying to get across that 135 calories in a single Twinkie won't fill you up as quickly as 94-95 radishes or an entire unpeeled eggplant (both of which have roughly 135 calories). It's not bad logic, but possibly phrased wrong.