As a hard core player (40-50 hours a week, 2 raid teams, 22 hours a week in raiding . . . yes I run H-FL on one toon, then dive back in on another to run it all again on regular on my other) I feel that if you say you are casual you are casual.

It's all about mindset, I go from hard core to casual at the drop of a hat, and it's really not about play times at all, but instead how you play the game, and how you view that play. I tend to call my between relationship periods as hardcore (ie, I tend to play a lot of wow with my buddies) then as I start feeling more social again head back into the fray and watch my wow habit move down to 12 hours a week. My view of the game changes from those two extremes, right now I am min/maxing, tweaking, and just doing whatever I can for that H-Rag kill. When I get bored with the game (again) I will grab something from my stable of alts and go full on casual, pvp for fun (I know, oxymoron), collect pets, and def drop at least 1 raid team.

tl;dr you are what you say you are, I know casuals who play way more than I do