If you re-read the blog keeping what I just said in mind, you will see that it fits. And you will further see that your point is in complete agreement - the people who are perceived as having good management potential have a low correlation with actual performance.
The blog points out that this happens at the bottom level because people who are good at non-management tasks get promoted to management and may or may not be a fit. But as you go up the latter you find that a lot of what tends to get rewarded is visible success. Which gives an unfair edge to self-promoting narcissists who manage to make their occasional successes more visible than they should be. The result being that perception and reality tend to diverge.