My understanding is the car already had bullet holes in it (from the previous shooting) - in terms of the vehicle description.
Whether the damage was new or old, "a silver Chevrolet Cruze with gunfire damage to its back window" is a MUCH better description than, for example, "a silver minivan" would be. The police officer had enough information for a reasonable belief that the occupants of the car posed an immediate danger to others. At that point, a runner looks like a would-be killer trying to (1) dump the evidence, or (2) shoot anyone else on his list.