Kinda surprising to me that you can beat dumb luck in inaccuracy.
It shouldn't be. Assume that your pundits in general do no better than chance. In a large sample, some of them are going to have to have to do really badly. Even if your pool on average is better than chance one should still expect a few much worse.
That said, even given that, -8.7 by their metric looks really badly.
According to that study, being a lawyer by training was one of the things that caused predictors to do badly. Note that Cal Thomas doesn't fall into that category.
This essay exists as a large section of my page on predictions markets on
gwern.net: http://www.gwern.net/Prediction%20markets#1001-predictionbook-nights