Hi thanks for your question.
Restaurant food though claimed to be clean and fresh but sometime it is old cooked 2 to 3 days earlier and not well preserved resulting in growth of germs which produce toxins.The germs with toxins are responsible for infection of gut called gastroentritis and its consquences like pain vomitting and loose motion
.The preformed toxins are responsible for such a quick reaction as in your case.The other reason for pain abdomen after restaurant food is gastritis
caused bu lot of spices contained in restaurant food.Gastoentitis may be the cause in your case.
Hope this answers your question.