Yeah, that Wowhead article is a bit off. This for example;
Is arcane, not frost. I also think the blue breath attack shown was also arcane-based, not frost.
As for the lack of black dragon spells, that's also highly doubtful. The developers mentioned that the class uses the magic of all 5 dragonflights, so black dragon magic is more than likely make up the core abilities (which makes sense, because their creator is a black dragon). Also this attack;
Comes directly from Onyxia.