Sodium chloride is saline which repletes the electrolytes in the body lost through sweat, urine, tears etc. This is normally given intravenously and does not contribute to the bowel movements your father is having. People will have bowel movements despite not eating food – this is completely normal.
In your father’s case, he is post-op from stomach surgery which contributes to a post-op ileus (paralysis of his gastrointestinal tract). This ileus is temporary and as his anesthesia wears off, his bowel resumes peristalsis (rhythmic contractions to move food from the mouth to the anus). Therefore, he starts forming stools composed of retained fecal material (from the last few meals), dead cells that have sloughed off his intestinal tract, and bile acids secreted from the liver. The sodium chloride may be keeping your father hydrated and may have a very small contribution towards keeping the stools soft and preventing your father from becoming constipated but it certainly doesn’t cause bowel movements.