No, it's not. The alt-right uses anonymous web boards like this one (but not HN to my knowledge) to coordinate and celebrate mass shootings that are directly admitted to be race-focused and white-supremacist-led. (Edit: The alt-right does use HN to spread hate and their "ideology", but I have not seen direct specific calls to violence here)
> Groups labeled "white-supremacist" rarely even contain a large number of white people.
I don't see how this is relevant at all. Being white has nothing to do with being a white supremacist. There are lots of non-white white-supremacists in the world. You're using logical fallacies like whataboutism and appeals to false authority instead of debating anything of substance.