You are correct "Akuma"
Sgt Cedric Popkin knew it was his bullet that hit MvR.
My Grandfather was with him at the time. Popkin was a marksman, and he knew how far ahead of the plane to aim his Vickers gun to make the hit. I have visited Popkin's daughter in northern NSW a few years ago, and had a nice chat over a cuppa, but the family did not have a lot of detail about that day, because Cedric did not talk about the war, when he came home. Recently, a plaque was erected in his home town, which explains the story.