I think that's a common myth. There's no separate category for frozen pizza in Nutriscore. The categories are: general food, drinks, cheeses, and oils/fats.

Pizza producers can game the system somewhat, however, by adding ingredients that are counted positive (like protein or fiber) to partially offset "negative" ingredients such as sugar or saturated fats.

Dairy lobbying has led to cheese as a separate category and that milk is counted as food, rather than drink.