I saw the driver retreating and stepping backwards and acting in a defensive manner.
It is unclear from the video whether the driver actually hit the dog or not. He might have connected on the first swing, but not on the second.
They claim that the driver was a regular and had been on the property and dealt with the dog many times before. If that is true, I would like to see the footage. I doubt that they have it.
I don't like Jack Russells. They are snappy and yippy and sneaky, and you practically need eyes in the back of your head in order to monitor one. Granted they are small enough as to be incapable of doing serious damage, but getting bitten also puts the driver in danger of falling, spraining an ankle, twisting a knee etc.
It is entirely probable that the dog was in fact being friendly, but the drivers actions were defensive and consistent with trying to avoid being bitten. Its not like he pounded on a poor helpless animal. This is just an unfortunate occurrence, and part of the risk one takes by owning a dog.