So the scenario is:

If you don't defect -He defects first: You may or may not go to prison -He doesn't defect: You may or may not go to prison

And if you defect first -He defects second: You don't go to prison -He doesn't defect: You don't go to prison

Still seems to me that the Nash Equilibrium is to defect. Not going to prison is better than probably not going to prison. According to the article, they still don't talk to each other, so it's not like the outcome would have changed much.