I think you are correct. They believe this is normal and this is real food. Not trying to hate on pizza. I love pizza (in moderation of course) but yeah, they think if you are thin then either your metabolism is just amazingly fast or, you are anorexic or something.  If they see you eating it's the fast metabolism if you tend to skip lunch or avoid eating in public (as I do because of all the unwanted commentary from fats) then you are anorexic.