I imagine that the image used on that page is from an older version of ACF. It was just caused by setting all of the fields to 50% width which would cause sorter fields to stack up against the taller field because they were all floating to the left.
ACF now adds CSS and classes to fields so that all of the fields placed side by side are the same height as well has adding a clear to fields that should start a new row. It appears that this is done with JavaScript.
To get this effect with the latest version of ACF would require adding your own classes, CSS and possibly some JS.
