Note that “public forum” is a term of art in First Amendment case law that refers to a venue owned or controlled by government, including a privately owned venue over which government exercises some control, made available for general or limited public discussion; the first amendment limits what government can do in such forums.

And this status is not an unprecedented one for government-controlled social media accounts; while the Trump case at issue here is the highest profile one to have reached a decision, it is not the first to find a government agency’s or official’s social media account to constitute a public forum in which viewpoint censorship by government of other users is prohibited.

Also, the decision constrains Trump's behavior on Twitter, it does not mandate any change to Twitter features.