No, it was the fact that you were shooting at 100mm and your shutter speed was 1/60th of a second. On a crop frame Nikon you were roughly at 150mm and your camera probably had some shake when you actuated the shutter. Not to mention you were shooting on f/20 which may not be optically prime. But you were in shutter priority and there wasn't anything your camera could do differently to get the proper exposure.