The Santa Clara County Fairgrounds is not a private establishment. This ruling is flawed, but it does have the benefit of making it impossible for the anti-gunners to appeal the incorporation ruling.
That's a very good point. I am delighted to see incorporation, even though I think that the clear language of the Second Amendment means what it says:
A well regulated Militia, being necessary to the security of a free State, the right of the people to keep and bear Arms shall not be infringed.
I personally see that as a proscription on all gun laws, whether federal or state (although I am aware that there are other people who only see that as forbidding the federal government from infringing on the RKBA.)