Not necessarily a secret email. When I created a YouTube account it also automatically created a google account as well, or forced me to? Does that mean I have a gmail account as well? IDK, but probably. And my yahoo account is somehow linked to my Windows Live account which was somehow automatically created when I upgraded my OS. I don't even know WTH Windows Live is!
Sorry that is not super helpful, but just wanted to point out that it IS possible there is nothing nefarious going on.