The point is this: normally, when a CGI script generates a page, that page doesn't actually "exist", it's only shown in the browser of the person who has requested it, the page is not written onto any hard disk. That's what's meant by "on the fly".
By the sound of it Tim Schulte's script actually writes HTML pages onto the hard disk. This message board behaves the same. The CGI script actually writes HTML files onto the hard disk instead of temporarily "flashing" the output in the browser which is what most CGI scripts do, and why robots ignore them.