? 

 The reason it sounds confusing is because it is, bulimics can have anorexic tendencies and anorexics can have bulimic tendencies. But a bulimic with anorexic tendencies is not considered simply anorexic unless (or until) they fit the definition of that disease. Therefore, a bulimic who engages in anorexic behavior is still a bulimic until they meet specified criteria. Make sense