“A member of House Velaryon not being a Valyrian”
By this I can only assume they mean that they’ve cast a black actor (Steve Touissant) to play Corlys Velaryon, who in the books has white-blonde hair like the Targs.
Think there’s a misunderstanding about the “Dornish knight” serving the Iron Throne, the PR has described Cristen Cole as being “Of Dornish descent”, I assume this is a mix-up since he’s from the Dornish marches (Blackhaven in The Stormlands, on the border with Dorne).