Because the camera lens was not in free-fall. The camera lens was attached to a person who had just moments before opened his parachute.
And, in fact, just before opening his parachute, the person was not even free-falling, but was actually wearing a wingsuit. (The parachute will have made the vast majority of the speed change here, though.)
Edit: Also, note that you cannot tell the speed of the rock without knowing either its size or its distance from the camera. If it's a big meteorite, it must be further away and be falling much faster. If it's a small pebble, it must be closer and must be falling slower. This stuff is covered in the Bad Astronomy article, and the Facebook post. In the latter, it is calculated that, if it's a near-by pebble, then it is falling just 10 m/s faster than the camera.