Obviously there's something in the database, since the forum works right now. If there truly wasn't anything in your database, the forums would not work.
If you refer to cPanel saying it contains 0.00mb I believe that is a setting that we opted to take out to reduce the stress on the server, if I'm not mistaken that size note is calculated and uses mySQL queries to do so.
If you refer to something else, please describe in more details what you mean by "there's no files in my database"?