Actually he did say that exact thing. RBG thinks he did, and I agree.This is way too heavy-handed, I think. @TheArbiterofAwesome did not say RBG was a revisionist racist, only that the denial of "intentionally manufactured genocide" is such a notion.
I too consider the claim that Native Americans were not subject to genocide at least inspired by racism, but it's a very pervasive notion in the public, so holding that idea doesn't make the person a revisionist racist. Similarly, I wouldn't consider a Turkish person a denialist bigot simply for denying the Armenian Genocide, since the nationalist revisionist notion that the Genocide didn't occur is very pervasive in the Turkish public.
As far as heavy handed - Heavy handed might have been to simply Ban him (which, BTW, has been done more than once in Chat for this sort of thing) without allowing the opportunity to prove his accusation.
As far a denial of the Armenian Genocide, that IS A Banning level issue, not an InstaBan, but not somewhere folks want to go. Not Even Close.