Heh, well that'll teach me for not being more precise in my wording. Of course your fitness level will have a positive effect on your mental abilities. What i meant to highlight was his use of specific insights _about_ strength training that he then found could be abstracted and applied elsewhere. The same possibility of which he had dismissed in the puzzle solving case.
I do think that collecting anecdotes from other fields can help you think better in your own field of work. I'm just not so sure that, for example, doing Sudoku makes you any better at thinking about things. Brain training exercises aren't general enough.