Does the cardiac sphincter keep food boluses from reentering esophagus once inside stomach?

No, the cardiac sphincter prevents the reflux of gastric contents into the esophagus, not the entry of food boluses from the esophagus into the stomach. The esophageal sphincter, also known as the lower esophageal sphincter (LES), is responsible for preventing the backflow of stomach contents into the esophagus.