With mobile adaptation implemented blocks and elements are repositioned in order to make reading the page easier and more pleasant.
Why this is cool
Repositioning
When small width of window makes it impossible to comfortably position all elements in a single row, here comes another version of the page that perfectly solve this problem by positioning elements in several rows or even in one column - another direction. The browser automatically detects the size of the window and decides which version is to be applied.
Try to decrease your window size. At some point left part will move to the bottom and will appear after main content block. And there will be another point (500px) when all blocks will be placed in one column.
This is very cool
All users despite their device screen's size will have fun reading that adpative page!
Click on the link in the navigation to see the same page without mobile version implemented - it is horrible ;)