I would guess this is a dosage thing. Here are a couple of things to think about:
1. Why is it that young men with high testosterone levels aren't dropping like flies and atherosclerosis is mostly a disease of the 40+ crowd?
2. If you push your testosterone above 1200 ng/dl, there is evidence your HDL will start dropping.
Seriously, are the authors arguing that low testosterone will be good for heart disease? Just doesn't make sense.