Partly its because you are still being interviewed.  You'll be talking a lot during the meal.  Keep it simple, easy, and pick something that neither has a strong odor, or is messy.  It also shouldn't be something that is difficult to eat. You're making an impression, and you want to appear engaged, normal, and likable. Something you eat with your hands is a bad choice, too messy.  Something that will slop out of a bun onto your plate is bad for similar reasons. It's all about impressions.  We're terrible at assessing other people.  So it's a good idea to make the best impression possible and adjust that impression in a positive manner.