It isn't contradictory. The french did colonize vietnam and force cash crops on vietnam ( like all colonial empires did ). But during the indochina war ( 1st and 2nd ), vietnam's coffee industry ( and all non-war related industry ) crashed due to the war itself and sanctions levied by the US/France. Vietnam was pretty much barred from trading with the western world, their primary market.
As the indochina war drew to a close and the coffee industry revived because of friendly soviet-vietnam relations and the opening of markets in soviet dominated europe. It wasn't just coffee, lots of vietnamese immigrated to soviet dominated to work and study as well. At one point, the largest non-white communities in eastern germany, poland, etc were vietnamese.