pages that are created based on the template in this way, are not physical pages.
They are virtual pages that are stored in the content management system
there is one physical page, and the different page content is called based in the querysting variable that is passed. for example:
Custom Pages=5
calls the content for one page
Custom Pages=4
calls the content for a different page.
in both cases, the physical page:
page.php
is loaded to the browser, but the querystring tells it to load different content into the page.