You didn't enjoy the benefit of being able to compare the two ideas side-by-side? They both neatly fit the screen in most resolutions if your browser window is max height, no scrolling in that particular case.
Beautifully designed article and your specific example is a great attention to detail on the author's behalf.
Three things: 1) I (and other people) like to scroll the page as we read so our eyes stay in a relatively fixed position and the text moves under it. 2) Plenty of monitors can't fit those entire sections. 3) Those two sections didn't benefit much (if at all) from side-by-side comparison.
Beautifully designed article and your specific example is a great attention to detail on the author's behalf.