Yep, it seems contradictory. How can communism have allowed such people to accumulate such great wealth?
Life is full of dialetical contradictions and while communism is premised on a classless society, fhe socialist state of development accepts the existence of classes and inequality as a fact of life.
The mistake you're making is in believing that the Chinese Communist Party has had any ideological relationship with Marxist economic theory since about the death the Mao.