IF your parents put you on as an A U the bank will match your name and their address. If the address is anywhere on your report (even as previous) thats how they access your report.

I attempted to "hide" a 20k balance by moving it to my dad's new account however it came right back on my report because I was an A. U. Most banks however, are pretty good about removing the A U promptly if you notify them that you want it removed. First USA requires the primary to call to remove the AU on their accounts. In your case however it will most likely benefit you to have the A U providing there are no lates and the balance is fairly low.