I dont think this protocol means the same as that for politicians etc. According to regulations, a pilot cannot fly for more than a certain number of hours, and must rest for a certain time before taking the next flight. Chances are, this flight went from Lahore to Doha, and then was heading back to Lahore with the same crew. Quite likely that the pilot would have exceeded his flying limit if he had flown from Sialkot to Lahore.
PIA probably failed to provide an alternate crew for the flight to Lahore.