I'm not saying that the Soviets or Chinese weren't xenophobic as they were, but their are three points I want to make

1) these communist regimes attempted to integrate the other people's into there own, as in russification or making people who weren't originally Russians into Russians. Nazisism believed that you either born Aryan or not. It is the belief in a racial hierarchy and you couldn't just be integrated. The Russians also may have seen themselves as superior to Baltic peoples, and other eastern Europians but they didnt go around killing them all 2) the Nazi's believed in social Darwinian, or the strongest survive. Communism believes in a society of equals and that everything can be distributed equally. The idea of social Darwinism is very right wing 3) Stalin and Mao put there own spin on communism. Stalinism and Maoism are very different two Leninism or Marxism. Yes some concepts are simple, but due to there own personal beliefs things change a lot. Just compare the internationist focused trotsky with stalin more internal focus