I'm surprised changing emails works that way; seems like a bug in the forum software.
Also surprised his username was available.
It is intentionally set up that way. I don't know why, but a change in email address requires manual reactivation.
The bug seems to be in how it notifies the admins...I've gone in to activate a brand new account, only to see that someone changed their email two or three days ago and has been waiting for their account to be reactivated. It seems the site's registration system does not flag up email changes in the same way as it does new accounts, despite it all falling under the same general administrative area.
Real pain in the arse, actually.