It's assumed that Faol was part of the scourge at some point, which is why wowpedia put it there. Fan wikia are havens of fan theories & headcanon. But its never specified in game if that ever happened. Just like how we see new undead pop up throughout the timeline that act independently of the Lich King.
Also never specified: That the plague of Undeath has anything to do with domination magic. Because how would it? We even see a completely separate source of undeath in Maldraxxus. You're just doubling down on your theory when there is no direct correlation.