Just as the Meyer lemon is not a lemon, the cocktail grapefruit is not a grapefruit: it's a cross between a mandarin and a pummelo. Since a grapefruit is a cross between a pummelo and the sweet orange, you can see why there are some similarities. But both the pummelo and the cocktail grapefruit lack the true grapefruit's characteristic bitterness: the cocktail grapefruit is instead a sweet, juicy, low-acid fruit with a mild grapefruit flavor.
(An easy way to cut supremes, as you can see, is to "carve" the grapefruit like you would a pineapple, and then slice the segments out in wedges.)
The cocktail grapefruit supremes were part of a composed salad, if you like that term: blanched charred chilled Savoy cabbage, lamb's lettuce, three hard cheeses (Pecorino Romano, gouda, cave-aged gruyere), bresaola, salami, cocktail grapefruit, cocktail grapefruit/lemon juice, hazelnut oil.
(Bresaola is sort of like beef prosciutto, though it's not especially salty: air-dried lean beef, sliced tissue-paper-thin.)
