There are a few side tangents that maybe confused you. Here is just the main argument with tangents elided:

>... The California legislators ... tried to get around the obvious First Amendment issues by insisting that the bill was about conduct and design and not about speech. But as we pointed out, that was obviously a smokescreen. The only way to truly comply with the law was to suppress speech that politicians might later deem harmful to children.

... the court saw through the ruse and found the entire bill unconstitutional for the exact reasons we had warned the California government about.