Sand - 2:21 pm on May 22, 2012 (gmt 0)
He thinks that because of this increased exposure, you are showing up for less relevant terms and the CTR is lower
This is most likely the correct answer. For instance, a friend of mine wrote a post about blue widgets. Being the good guy that I am, I plussed his content. Now, I see his post every time I search for anything remotely related to widgets.
I'm never going to click that post in the search results, because I've already read it and know that it doesn't answer the specific problem I'm trying to solve. His CTR probably looks terrible, but the exposure could be helping him on a personal branding level.