I don't know what book you are referring to, but it sounds as if something had happened which was so shocking that everybody in the cafeteria--customers and employees--were frozen with fear or amazement or some other emotions. Then gradually the people began to resume doing whatever they had been doing before the traumatic event occurred. It sounds as if it might have been a robbery or some other act of violence. It is an interesting metaphor. We can visualize a cafeteria with people pushing their trays along a serving line, others eating at tables, employees in their white coats and white caps waiting on customers, clearing off tables, etc. The fact that the cafeteria came back to life slowly suggests that whatever stunned all these people must have been quite a dramatic event.