Probably because he is clueless, and just rewrote something written by someone else that is clueless.
From my observations, “sites”, do not have authority only individual pages. So if pages are linked together on a site, authority from individual pages can be passed within the pages of a site, just as it passes between pages on separate sites. If you create a new page on a new site and get a link from a page with authority, that authority page will pass the same amount of authority to the page on a new site as it does for a new page on the same site.
