In this case, it's semi-justified by the fact that a bunch of the page is large images, it's basically a page of presentation slides. Would be very hard to read on mobile even if the layout wasn't broken.
(Obviously, the ideal is a page that actually reflows, but the problem of accurately reproducing slides on mobile is a difficult one.)
Web devs, please don't go out of your way to forcibly break the browser's layout engine.