What it plots are the average verbal and math components of the GRE for a variety of subjects. If you are applying to grad school in physics, you are likely to be in the upper right hand quadrant--good verbal and math scores.
I've marked the fields of Taubes and Guyenet on the plot in green and pink. Green is neuroscience. As you can see, Guyenet is likely to be smart. However, the two pink circles are aerospace engineering (which Taubes studied at Stanford) and History of Science (which he's basically been engaged in during his professional life). As you can see, Taubes is likely to be smarter, or perhaps more likely to be smart, depending on your perspective.
Actually, this doesn't come as any surprise to me. While I suspect Guyenet will come out on top in the insulin-obesity wars, I think, taken as a whole, Good Calories, Bad Calories is more "genius-y" feeling than Food Reward Theory. This probably demonstrates that Taubes is a very smart guy who has been working in journalism too long, while Guyenet is fresh off his PhD work.