That's kind of a big deal because CA is a state where DV is a crime against the state, not the victim (so victims don't have to testify and there are often cases where the victim is opposed to the prosecution. Happens)
As well, if the facts warranted prosecution, especially in CA, you can bet that it would be due to the local pressure.
If he's not prosecuted, it would seem that the facts didn't warrant prosecution. No DA wants to be protested or be branded a Friend of Abusers...