I'm guessing he means accurate medieval demographical representation. Don't mind TOO much myself, but it would feel a bit weird with a modern post-globalist society in, for example, the shire. I'd welcome darker skin stones in Gondor, considering they are basically bordering the "not-Middle-east" and by extension, "not-Africa". It's unfair to call people who care about authenticity and realistic population in a carefuly crafted world racist, just as it is unfair to degrade people who don't care all that much about skin color in fantasy.
Basically two poles at war here. "Realism" vs representation. GOT is a representation of the former, as it depicts European middle ages. Latter, well, there are countless fantasy series who has no qualms with adding a modern, particularly American, society in a medieval setting. Nothing wrong with that in of itself, but these series are rarely that good - which is cause for worry.
Also, why not rather develop the cultures known to be dark-skinned and work them into the narrative... Tolkien kinda forgot them in all this. That would be a lot more interesting.