Is Heidi Klum really as sweet and loveable as she appears in Project Runway?

Whenever I watched the show, it always looked like the designers were so fond of her, and she always seemed so kind. Then in the episode before the Olympus Fashion Week exhibition, one of the designers who was eliminated earlier said something like, "Heidi, I love you" and she gave him this unreadable, kind of forbidding look. I had thought that she was one of the few supermodels who wasn't a diva. Was I wrong, or was that particular designer just really mean to her?