Chandra's remains were covered by about 12 inches of brush and leaves. The leaves fell in November (some of the remains were not disturbed by the turtle hunter, and the leaves date the placement of the body at least back to that time. They were also covered with some soil, but this might be due to settling and weathering - they might not have been buried "in a shallow grave" as was earlier reported. On the other hand, the killer might have made some efforts to hide his kill.
Old turtle (tortoise)shells do get covered with soil - I used to hunt for them myself when I was a kid. They would be somewhat embedded in the dirt/humus in the woods.
The guy wasn't digging, he was just looking for turtles. The dog took off after catching a scent, and it was the dog that started digging.