Well Re-post it in the drama
There is no reason to repost this nonsensial topic anywhere.
You cannot grant yourself admin. Either you have an admin password set (not recommended) and he guessed it or got it from someone else, or one of your super admins gave him admin. Or you have a crap-on on the server that granted him admin. Always be cautious with private add-ons, they sometimes contain backdoors as there's no backdoor checking by RTB moderators and no reputation to lose because there isn't a forum thread where someone could point it out.