Randy described the two on Facebook. The lower rating is the stall torque (as in the servo can hold its position up to that much torque). The dynamic torque is how much force would be required to stop the servo dead in its tracks if it was moving at full speed.

Quality brand servos typically use stall torque for their numbers. Cheap brands/knockoffs have been known to use the dynamic torque numbers to inflate their perceived performance. Nothing wrong with including both, as long as people understand what they mean.