How come Vietnamese communism was comparatively mild?

Ho Chi Minh did very little to help the Allies in WW2. He came back to Vietnam in early 1941 and help set up the opposition to the Vichy French and Japanese but the only real contribution to the war effort was passing information to Chinese intelligence. In 1942 he was arrested by the Chinese and held for two years. He returned to Vietnam in September 1944 but the only contribution to the war effort was intelligence and the occasional rescue of a downed airman. He declared a revolution against the ruling Japanese in August 1944 but the war was pretty much over at that point.

The Vietnamese did not embrace communism as a method to achieve independence, Ho Chi Minh was one of the founders of the French Communist Party and had studied in the USSR prior to coming back to Vietnam.