In September1945 Ho Chi Minh announced the formation of the Democratic Republic of Vietnam, Truman, Churchill and Stalin had already agreed the future of Post War Indochina, The north would be occupied by China and the South would be occupied by the British, this I assume is why your man was in Vietnam, however the French tried to reclaim their former colony and the British left in October/November presumably for the nearest bases in Hong Kong and Singapore.
The French were finally kicked out in 1954 after the disastrous battle of Dien Bien Phu.
James