At that point it's a legal public byway. Kind of how easements etc are.
He's allowed to have a gate, but he can't actually block access. He also knew this when he bought the place.
Of course hopping the gate isn’t illegal so...
Yet there's a near universal consensus that "the law" (i.e. the founding statutes regarding access to coastal properties, from the time California entered the Union) mandates that this access must be maintained, for perpetuity, by whoever takes title to the property.
So in effect there's a permanent easement attached to the property (even if the term as such didn't appear in the text of the original statues).