I would theorize that they have GPS in both units, and the tag sends its position to the base. Along with a compass, you can pretty accurately tell where the camera is looking, and you can probably gauge the distance between the tag and camera by the time it takes for the signal to travel to the camera, but I'm not sure how that's useful.
According to some of the amazon reviews, it doesn't work within 50 feet. I suspect it does in fact use GPS, as 50 feet would be far enough that you're going to be somewhere in the frame. Couple that with just measuring the delay time, and possibly a compass or something and you'd end up with what they have.
That's what I was thinking. Both are viewing the same satellites, since they're close to each other. The base, since it knows it's stationary, can derive the corrections itself, and figure out where the object is.