The hose for the Hurricane pilot's oxygen mask changes position between shots. Sometimes it's correctly downwards. Sometimes it's pinned to his shoulder and you can see the end of it and that it's not connected to anything. And, sometimes, it routes over his shoulder to the rear of the aircraft.
When David's plane is damaged by AA fire, he is last shown in the cockpit at treetop level. When next seen, he is on the ground still in his parachute harness, parachute deployed. He could not possibly have bailed out at the altitude shown.