I don't mean to suggest that walking and thinking is useless. It's quite productive, actually. But theoretical hacking will only get you so far. Sooner or later you have to type things, and read the results, and read the manuals and blogs that explain the results, and I can't really do much of that while strolling around the block.
I think that the point of the article was that taking a stroll now and then does not offset the 'damage' done by sitting. They were pretty much tearing into the idea that you can offset the amount of sitting/inactivity in your life by exercising to try and create some sort of canceling or equilibrium effect.
