When the onions and apples were cooked there was a layer of cooked on brown stuff in the bottom of the pan. This brown stuff is flavor! Basically, it's caramelized sugars and proteins (Maillard reaction things).
2oz of apple cider and 2oz of chicken stock were added to the pan. The liquids immediately boiled, loosening the brown stuff in the process. The liquid was reduced by half and 2oz of half & half was added.
Then, the pork was transferred back in the pan to heat up.