An explanation for mobile phone users 

The page you have seen is either the third, fourth or last version of the same page which is intended to show to a desktop user what is possible with a responsive site, and how different information can be shown to users of different devices whilst still being on the same website page.  
As such its best viewed on a desktop or laptop, then by following the instructions you will see the page change as the screen width is reduced. 
On a mobile phone, if you rotate from portrait to landscape or visa versa you will notice a change on the previous page, but the text information really only makes sense when you start on a full width laptop / desktop.