The unit of a "cup" there is sourced from the US government, and thus it's well known to be a volumetric measurement that is equal to 1/672 of a standard oil barrel's volume. It's not vague for US customers at least.
It hurts my soul that it's using a volumetric measurement for leafy food, like if you cut lettuce leaves into pieces, they have the same nutrients but take up way less space, so 3 cups of roughly cut lettuce leaves is different from 3 cups of finely chopped lettuce leaves, which is also different from 3 cups of uncut lettuce leaves. Just give it to us in mass or calories please (like grams or fractions of an oil barrel's mass, or fraction of a barrel of oil's calories and nutrients).
But, wow apparently the FDA rounds cups in nutrition labeling to be exactly 240ml “legal cup”, which I agree is super annoying. It’s 1.4% more.
“For purposes of nutrition labeling, 1 cup means 240 mL, 1 tablespoon means 15 mL, 1 teaspoon means 5 mL, 1 fluid ounce means 30 mL, and 1 ounce means 28 g (21 CFR 101.9(b)(5)(viii))”
It hurts my soul that anybody producing a table such as that is using something as vague as a "cup" in their calculations.