They claim to be the only real leftists, because communism requires putting down revolutions with tanks and supporting genocidal dictators. They call it “the dictatorship of the proletariat”, where proletariat means worker. They think a dictatorship can be leftist.
Read The Player of Games by Banks
EDIT: Okay so I actually read the first three paragraphs, and no. On Authority isn’t relevant. Engels is using a different definition of authoritarian than I am.