The right sentence, though I'd make him the attack dummy for the local K-9 police dogs.
Not necessarily. The dog was a rescue, and he had only had it for a short time. Rescues sometimes come with some very difficult issues that take time to work out. Some dogs run away to assert their independence, or just because they like to run.
That said, the man was a fool to have a recently adopted dog (with possible issues) in his vehicle without having it crated or attached to a seat belt. At the very least, it should have a 20' line on its collar at all times until he's sure it won't run.
BTW, I have never hit my dog (other than cuffing her under the chin with an open hand for a serious offense) and I would certainly try to stop anyone who was beating an animal. But I don't think this sounds like a felony.