The Lemmy software is intended to be somewhat censorship resistant, but that does not mean that lemmy.ml is a “free speech platform”.
Like most instances, lemmy.ml has rules (they’re in the sidebar on the front page) and we regularly delete posts and comments which violate them.
That instance you’re talking about is intended to be a “free speech platform”, which in modern internet parlance is a synonym for “nazi bar”. One of the two admins of that instance says explicitly: “racism, bigotry, sexism is allowed".
Most Lemmy users aren’t into racism, bigotry, sexism, and the other things people there are into, so, most Lemmy instances have defederated them.