Was it truly and completely black or was there some ghosting of light or the image?
1. Aperture block problem images aren't black, they have a ghost of the actual image with very deep DoF (because the aperture was incorrectly narrowed to the smallest setting).
2. Mirror problems tend to leave a faint ghost of light at the upper-edge of the image because some light gets past the lower edge of the mirror.
3. Only some shutter and sensor problems may be totally black.
P.S. Check the EXIF on that image: it may show that something (or someone
used a very strange exposure setting.