I recently removed moderator permissions from a user. Admin cp no longer lists them as a moderator but this member had a custom title of "Moderator." I was wondering if this was a carry-over from vBulletin since all my moderators have this custom title.
If it is defined as a custom title, then the groups they're in won't matter; the title will always be used. You can check this while editing their profile in the control panel. Otherwise, the title would be coming from a group they're in.