Nearly a half of all awards of the George Medal to date have been to service personnel (c. 850), so Crabb's award is not particularly unusual. Not sure if he was RN or RNVR but the latter were certainly not classified as civilians. The George Cross is an extremely scarce decoration (also awarded to both service and civilian recipients). It ranks immediately below the Victoria Cross, so conditions for its award are particularly stringent and presumably Crabb did not meet the criteria for the higher award.
Incidentally we had a station commander at Marham with the George Medal, Gp Capt Vic McNabney. He had won it as a Flying Officer when attempting to rescue a glider pilot who had crashed into a waterfall.