No you do not have to order from the menu. The only time you would have to pay at a restaurant to be seated is if it is a buffet or a dinner show. You are free to not order anything, or just have an appetizer, or just a dessert, or just a soft drink, or if you wish, a full meal.
Sometimes my stomach is off and I don't eat for awhile. Well, my son has asked to eat at Be Our Guest for dinner. If I am not up to it, do I have to order something to eat?