Paralytic ileus can sometimes happen after any operation on the abdomen, whether or not the surgery was done for cancer.
During the normal process of digestion food is moved through the intestines by waves of muscular contractions in the wall of the bowel, which squeeze the digestive contents along.  These waves of muscle movement are known as peristalsis.

A paralytic ileus occurs when there is a failure of the nerves and muscles producing the peristaltic waves.   This means that the normal contractions of the bowel stop and the bowel contents become stuck.   This leads to a build up of gas and fluid in the bowel.  This in turn causes swelling of the belly, sickness and vomiting and constipation.  Despite these problems, a paralytic ileus  is not usually painful.

There are a number different causes of paralytic ileus but the commonest is an operation on the belly.  The condition develops immediately after the surgery, becoming apparent within 24 hours or so of the operation.  Any operation on the belly can lead to a paralytic ileus.

A paralytic ileus will nearly always settle down and disappear on its own, without any treatment.  This may take a day or so and during this time it is usual to stop the patient having anything to eat or drink giving fluids and minerals through a drip into a vein in the arm.Once the paralytic ileus is over recovery back to normal is very rapid and there are no long lasting ill effects.

So your father was unfortunate to have this complication after his operation, but it will not have any effect on his cancer and should not affect his overall recovery in any way.