Industrial agreements and CAA/EASA regulations require there to be rest seats for the pilots on long sectors. In reality, most of them use the bunks and not the cabin seats. As a result, the flight crew on the day often (and kindly) release these seats to those on staff travel at the discretion of the Captain.
These seats are never commercially offered to passengers, are not available for booking, and are not part of the seats available for sale. As such, I wouldn't concern yourself too much with who is in them or for what reason.