re: Does the running game open up the passing game or vice versa?

Both. You need to force the defense to defend the entire field. When Harris stood on the left hashmark and threw a fifteen yard out to Quinn on a rope to the opposite sideline he sent a message to the defense. He can make every throw, so you can't cheat on your coverages or stack the box because he will make you pay.

That opened up the running game. This isn't rocket science. if the defense has to defend both the pass and the run, they will defend neither as well as when they can concentrate on defending only one.