Two different organizations. You seem to be referencing this article by James Zwick . Since he also wrote the article that connected Masters with the communist-supported organization I don't think that he would make a mistake and place Masters in the wrong one. Try here .
...which would indicate only that he consistently participated in anti-imperialist movements from roughly 1897 through the 1930's. You are still unable, however, to produce evidence that he ever held any communist political beliefs or was ever directly affiliated with the communist party like James McPherson is. In fact, the very same year your source dates for Masters' involvement in the second group, 1928, is the year that Eugene V. Debs' lieutenants were writing him and telling him that the communists no longer had control of the anti-imperialist league!