But you specify the maximum that you are willing to pay per click. Presumably he knew what he could pay per click for average users while maintaining profitability, and set the maximum accordingly. He doesn't seem to have a problem with his cost per click.

The point of the post is that the "users" became increasingly less valuable as the volume of clicks he purchased rose. It shows that you cannot obtain large numbers of legitimate clicks/likes through FB ads. As the reach of the campaign grows, the percentage of authentic users clicking on ads appears to rise dramatically. That is a huge problem. My personal belief is that the percentage of fake accounts and bot activity is far in excess of Facebook's estimates, and there is little that they can do about it.