They are saying to farmers in other states that you must comply with our regulations if you want to be able to ship your product to our state for sale.
That is interstate commerce.
You'll see more and more of this strange way of thinking coming out of California as Americans become a smaller and smaller part of the political culture.
Remember, Latin law says the fruit on a branch belongs to the guy who owns the trunk. American law says the fruit on a branch belongs to the guy who owns the land directly under that fruit.
They simply don't think the way we do on so terribly many basic ideas it's unlikely they can ever be assimilated.
Then no other state sells to California.
It really is that easy.