[Bombphoon]

A bit of scouting (cut and paste) online and in books:

It turns out Hubert von Greim was the only son of Robert Ritter von Greim (22 June 1892 – 24 May 1945), the German Field Marshal and First World War Flying ace. In April 1945, in the last days of World War II, Adolf Hitler appointed Greim Commander-in-chief of the Luftwaffe (German Air Force) after Hermann Göring had been dismissed for treason. After the surrender of Nazi Germany in May 1945, Greim was captured by the Allies. He committed suicide in an American-controlled prison on 24 May 1945.

"In late 1942, his only son, Hubert Greim, a fighter pilot with 11./JG 2 was listed as missing in Tunisia."

"von Greim a Bf-109 pilot with 11./JG 2 "Richthofen" was listed as missing in Tunisia. He was shot down by a Spitfire flown by a Royal Australian Air Force pilot, Flt.Lt. Robert Maxwell Brinsley, but bailed out and spent the remainder of the war in a prison camp in the United States."

"The young von Greim, of 6/JG53, had crash-landed at Tabarka after his Me109's cooling system was damaged in combat with RAF fighters on 31st December 1942. He was shot down, but bailed out and spent the remainder of the war in a prison camp in the United States.'

However, the Osprey book on Jagdgeschwader 2: 'Richthofen' solves it: in summer 1942, Hubert von Greim flew Fw190A-3 Stab JG2 from Triqueville, so it seems likely the machine-gunning incident mentioned was on a hit and run mission (presumably he was held at Trent Park before being sent to the US as a POW?) - but that leaves the mystery of where/when this incident happened 'near Eastbourne', which presumably, must have been witnessed by many?