We have "murder" and "manslaughter" - two forms of homicide. Wikipedia tells me the distinction goes back to at least the 7th century BC.
In US law, both have multiple nuances; first- and second-degree murder, and voluntary and involuntary manslaughter.
I interpret the argument as wanting to reserve "racist" for systemic and institutional racism.
We already have other terms we can use. For example, the law talks about discrimination on the basis of race and color as well as national origin, sex, or religion.
So, why not use "discrimination on the basis of race" or "racial discrimination" for the non-systemic kind, and reserve "racist" for the systemic one?
Even better, there's no reason to use "reverse discrimination on the basis of race" because that's identical to "discrimination on the basis of race."
FWIW, in my understanding of the issue, as I described above, I'm perfectly fine describing the US treatment of Mormons as racist - "white-on-white" racism - being also highly aware that Mormon religion was itself highly racist against blacks.
But the concept of "can't be racist against whites" isn't meaningful for even 100 years ago, because "whiteness" is such a slippery social construct. Finns were racially discriminated against, as the "Finnish race", and derogatorily called a China Swede, even though in the modern sense they are very "white".
As for "mostly a military coup" ... a genocide is by definition affecting a protected group - more specifically a national, racial, ethical and religious group. All of those are also protected groups under US anti-discrimination law.
If you want to argue that racism should be treated as a broad term, then genocide is a type of racism.
If you are arguing that my definition is wrong - congratulations. I'm a programmer, with only a lay understanding of the topic. My point wasn't to give an exactly correct definition but to point out an apparently deep misunderstanding of the issue at hand.