Agreed, for us, cold pizza taken to school would have been the leftovers from the hot pizza we had the night before, not frozen pizza or frozen pizza thawed out.

Now I guess you could argue whether or not it was frozen pizza that we baked in the oven or freshly made pizza from a pizza place but I don't think either of those matter since the end result is the same for both: cold pizza that was once full cooked and hot.