Well, it isn’t entirely fair to say that communism = authoritarianism. If anything communism is supposed to be very much an anarchy. That being said, Soviet Union collapsed into totalitarianism quite early in the century in the thirties because of Stalin (not communist ideology).
As to the fall of the regime. I do think that the point by the author is very relevant. It was a total reliance on one mode of economy, utter inflexibility and disconnect with the reality of the world that brought down the SSSR.