No one is arguing the State of California can't get the evidence. Just the law states you can't use warrants to get it from journalists, just subpoenas, to allow to filter out items from other sources/stories.
Federal law has an exception. State law doesn't have an explicit one.
If you read the EFF's post (linked above), there is a argument that the warrant runs a-fowl of the law. Not that they are immune to the law.