The claim that the DC-6 was shot down has been around for ages. The aircraft that supposedly did the shooting was a Fouga Magister. It has also been rumoured that the DC-6 was carrying arms and ammunition and that there was a survivor who was shot by people on the ground.
It is all highly unlikely. An aircraft shot down by machine gun fire will show the appropriate damage (the Magister was equipped with 2 x 7.5 or 7.62 machine guns each with 200 rounds, according to Wiki) and none was noted by the air crash investigators. What is more likely is that the crew unknowingly lost altitude in the circling approach and hit the ground short of the runway. It is a well recognised hazard of night operations into what is know as a "black hole", that is, a runway where the only lights are the runway edge lights.