When you had just 256 unique 8x8 pixel characters to draw all of the game graphics, you tried to use as few as possible. For drawing a thin line rectangle, you

When you had just 256 unique 8x8 pixel characters to draw all of the game graphics, you tried to use as few as possible. For drawing a thin line rectangle, you need at least 4 characters. Which are exactly the ones mentioned in the blog post.