As to why it was a through train from Leeds, that would be because they stuck it onto the end of a Leeds-Morecambe service. Northern have no crews based in the Lancaster area and so the Morecambe shuttle or in this case the Morecambe and Heysham shuttle has been worked by crews from depots such as Skipton, Barrow, Wigan (?), Manchester(various) over the years. The crew bring in a unit from their home base, or the far side of their home base, on a service to Morecambe or Heysham, and then most often double back to Lancaster before taking the unit home again in service. Long ago the unit stayed on the line and the crews came in passenger to change over. This caused utter chaos thanks to unpunctuality, crew shortage, unit failures etc.