This is because you cannot concentrate on your food as your mind is on fun and not on health. You do not keep a check on how much you are eating and end up eating at a faster pace, so you do not know the quantity you have eaten and come out stuffed and guilty. The loud music stresses you out and in stressful situations, you tend to eat more.
When you eat in a restaurant which plays soothing music, you are calm and relaxed and tend to eat slowly. Your mind in the relaxation mode will help you to concentrate and eat slower, have smaller mouth fulls and hence you will eat very less portions of food and still feel full as your brain takes 20 minutes to register that you are full and will finish later than if you listen to fast paced music while you eat.
So next time you plan to eat out and you do not want to binge, you know where to eat and still enjoy the experience.