You can see the 140 m wide impacted asteroid at the end of the debris field, the end of which has a strange structure (presumably containing the biggest chunks thrown out by the collision).

The small spot at the lower left end, which is the bright spot in the magnified inset, is the 140 m wide asteroid. The beginning of the comet-like diffuse thing is the debris kicked up, and the 'tail' is light dust, moving further with the help of solar wind, direct radiation pressure and the Yarkovsky effect (anisotropic thermal re-radiation of the absorbed sunlight).

When the object was discovered, it was indeed first thought to be a comet with a completely evaporated core, but a comet looked less likely when its orbit was found to be a regular one in the main asteroid belt. Then a ground-based large telescope discovered the small asteroid next to the tail, and Hubble revealed the X-shaped mark made up by the larger pieces of the derbis.

_{*Lunatic*, n.
One whose delusions are out of fashion.}