Harris does not think that and never said any such thing. You're literally making false statements and putting them in his mouth. Yes, he has discussed the social stratification of IQ scores. And for this, he's a racist? You just proved my point.
It's important to note that this idea about IQ is in fact a repackaging of race realism. In another decade Harris would've been talking about phrenology. It is an intellectual fig leaf for racism.
I'm not sure there's much daylight between "social stratification of IQ scores" as posited by Harris and "scientific racism". There seems to be a widespread belief that "scientific reasoning" is an inoculation against white supremacy (or any other kind of bigotry), but a bigoted statement rooted in a scientific claim is usually still just as bigoted.