Racism is the result of systems which disadvantage people of a given ethnic group. These people by definition cannot be victims of racism, because they come from the advantaged social group.
They are victims of prejudice. Prejudice born of the fact that they are the benefactors of a long history of racism in South Africa. While I am sure not all of them are deserving of this prejudice, I suspect the ones calling it racism are.
There's a massive difference between "believing you are the wrong gender is mental illness" and "being born/sorted into a gender that doesn't represent you causes mental illness." This is the latter.