Scrotal temperature and vascularization
The fingers and toes (for example) ARE at lower temperatures than the interior of the torso.  It's why it's so easy to get frostbite on the extremities. As for temperature regulation of the testes, you have to also consider that humans evolved without clothes...i.e. The testes just "hang out" and get lots of airflow, as opposed to modern times, when they are typically under (usually) more than one layer of clothing.

Also, for reference, I took some quick IR temp readings on myself:

Room temp: 19.9C

Fingertip: 27.0C

Palm: 31.8C

Axilla: 34.6C