Wrong! Thoroughly, totally, and utterly wrong!
Schmalfeldt has no First Amendment right to be on Twitter. No Twitter user does. The First Amendment secures our rights vis-à-vis the federal government and, by extension through the Fourteenth Amendment, the states. Twitter is a privately-owned enterprise. None of it’s users have any First Amendment right to be there. We use it at the sufferance of Twitter’s owners.
Bill Schmalfeldt, like the rest of us, has a First Amendment right to speak publicly within very broad limits. But Twitter has a right to tell him not to trespass on their site if they chose, and they have exercised that right from time to time by suspending some of his accounts.