He's not saying the race is stupid. He is saying that it is more stupid, an operant he expounds on, revealing his underlying meaning as both accurate and mild. A factual statement is not and is never denigration.

If you and you specifically were the sole member of a race, for instance, his operant would rank your race below that of Black. This would be an observation, not a denigration.

But, if you are not Black, you are the recipient of favorable averaging. Your race would be less stupid than Black, despite you.

I hope that helps.