That control lies more with Twitter itself and individual users.
Perry is simply inapposite here.
If Twitter automagically converts into a public forum when a public official uses it, then, axiomatically, the First Amendment is violated if the public official uses Twitter to impede speech he disagrees with.
Essentially, Trump is never "off" on Twitter, even though this too bizarrely curtails his own rights.
But, boy, they sure showed Trump!
The conclusion simply does not follow, and the court just runs right over the precedent because this is the conclusion it wishes to draw.
The nature of the property here is a private company, not public property.
The public character of the "interactive space" exists independent of the public official.