I would probably redirect and say something like "there are multiple variations and expressions of communism, and Stalin was just one of them, a more authoritarian expression definitely." And I might point out that there are people who think of themselves as anarcho-communists as well, and many other variations.

I think it's important to point out that there is nuance within communism and the methods of achieving a communist society, and to try to use examples that are less publicly associated with violence if possible. When you're talking to someone asking a question like that, it doesn't matter so much what sort of communism or philosophy you personally subscribe to, more that you are able to kind of soften it, in their eyes, so they might be more willing to learn more.