Is the esophagus a muscular organ? Why even in a patient lying totally flat on a hospital bed can the swallowed food reach the stomach?

The esophagus is a predominantly muscular organ so the assertion is correct. The esophagus is a muscular tube produced in its superior third of striated muscle tissue, in its middle third of mixed muscle tissue (striated and smooth) and in its lower third of smooth muscle tissue. The peristalsis of the esophagus gives the movement of the food towards the stomach even without gravitational help.