I can further increase you basis of a conjecture by including the support that players were also leaving other games such as GW2 and SWTOR (both of which stole a decent amount of players from WoW) and that further helped the re-launch of this game.
What your describing is the typical observation of the flow of content locust that plagues MMO's these days. The issue I have with your conjecture is that this flow of players is not in fact FACT. There is no way to prove the number of players coming and leaving this game simply based of other games success (and losses). It's still a conjecture all the same.