I think the author revised the figure(s) between the time of the parent comment (by gcr) and your comment. At least, the A * B = C figure's filename seems to imply a revision [1].

EDIT: yep, the figures were revised. Compare the corrected version [1] vs the original [2].

[1] https://petewarden.files.wordpress.com/2015/04/gemm_correcte...

[2] https://petewarden.files.wordpress.com/2015/04/gemm.png

EDIT 2: I completely missed that the author put a notice (about having revised the figures) at the bottom of the post.