The BCT DB was leaked sometime after you created your Dorky account and hence someone could have infiltrated your account, given that you had a sufficiently weak password. So... not an inside job. And it wouldn't matter that your password wasn't found on any other site.
And supposing that the account was sold for 0.3 - 0.5 BTC, I'm assuming that it was some time before 2017, where the price would be sub-500 for the account. There is no way that it would have been sold for such a ridiculously high amount post-2017.
I would like to have some explanation on why using email confirmation as a security measure is actually weak and unjustified, thus remain unused by Bitcointalk forum, despite it being so widely used by other websites.