Thanks for the link. Unfortunately without any details on the experiment design it's hard for us to get anything out of it. What was the task, who were the participants, what was their familiarity with the software they were being tested on?

I can say that this talk of using the keyboard being so fascinating that it takes up significant mental resources to be not represent my experience using and seeing others use keyboard-centric interfaces. When I use magit, or when I was operating the minilab I mentioned above, I don't have to think about what key to press to do the thing I want. I am in fact "so disengaged [with the mechanics of manipulating the interface] that [I] have been able to continue thinking about the task they are trying to accomplish". Competitive StarCraft is another example that illustrates the same point without relying on personal anecdote.