That is an interesting study. It resonates with me in some ways--I work in a culture where a loud idea is frequently presumed to be a good idea. The examples towards the end are more extreme. From my experience, it's less competent bosses who don't really understand the work they're asking others to do but try to act like they truly do.
I agree with you that a great leader doesn't need to be an expert, however, they just need to be good processors of information from experts with an exceptional ability to plot a well reasoned course based upon that information. You have to be comfortable admitting you're not the expert on specific topics but that you're still qualified to put it all together and call the plays.