I'm on a Retina Macbook Pro, and the white/black checkerboard square (A in Figure 12) matches the (128,128,128) gray (B), not the lighter one (C).

Looking closer, it seems like my computer is, like, anti-aliasing the image itself. In Digital Color Meter, the white and black pixels are both grays. See screenshot below, the magnified area is from square A in the browser. When I downloaded the image and opened it in Preview it is black and white like it's supposed to be.

Screenshot: https://cl.ly/2T2U2J0A3v31 (If you're on a Mac maybe try opening the image in an image viewer)

Anyone know what's going on? I also can't distinguish between the first few black bars in Figure 2.