My CharactersFollow

I play WoW and when I created my account, somehow this forum was able to determine all the chracters I play on. I can view these by going to My Account -> Your Characters. My question is how is this information gathered? I never typed it in, and honestly I am pretty upset that it was somehow magically shown there. In particular, two of the accounts that were shown there were on a totally different account! I don't even know how this information was collected, and I'm pretty upset over it, the only link between the two accounts is credit card information, and the other account has nothing to do with my presence on this forum. I have deleted the two characters in question from my profile on this forum, but I'd like some answers about how they got there in the first place.