I believe Arctic is correct in assuming it was a glitch. If a user has clicked on a link that was sent to their e-mail (one that was sent a while ago, before the closing of the Registration), it may have considered it as a new account. Keep in mind that when updating the forum, all forum nicknames were removed and reverted back to the user's in-game username, so what you see as being a new account may simply be the last account that you've seen in that area before, only without a forum nickname (making it appear as though a new account was made). If they have tried to register by clicking an old link or attempting to make one, this could be why it reads as a new account having been created.
Either way, I believe it is a glitch. Hopefully this makes sense. c: