Generally you write the Post-It, then peel it. So, writing with the adhesive on top, you could peel it from the side. But the article describes writing the note

Generally you write the Post-It, then peel it. So, writing with the adhesive on top, you could peel it from the side. But the article describes writing the note 90° rotated which is just odd. Edit: I was wrong—I see now the article is NOT implying that you write the note 90° rotated. But I agree with others that the photos are not communicating this well.