They did no such thing. That part of the bill concerned how much tomato paste has to be on the pizza for the tomato paste to be enough to count as a serving of vegetables. The USDA wants 8 tablespoons, and Congress wants 2.
There is no such thing as a 'vegetable'. Some are leaves, roots, tubers, gourds, stalks. Vegetables have always been an essentially tautological group.
Other fruits considered vegetables include peppers, beans and squash.
I actually believe pizza as a vegetable is easier to buy than what SOPA portends (plus pizza had the "ketchup is a vegetable" precedent). For that reason, I think its passing will be more contentious.