Mackenzie Scott will leave running the platform to the people familiar with it. That's exactly why she's the best person to own Twitter and turn it into a public good vs. Elon, who also knows absolutely nothing about running Twitter, but will no doubt intervene.
Musk made his comments in context of social networks. In a digitizing world where all conversation is centered into a handful of platforms, those platforms become the free speech carrier, no matter who owns them.
Yes, you're technically correct, but it's irrelevant from a pragmatic point of view. A legal definition of free speech is worthless if said free speech cannot be expressed in the places where most speech happens.
You can argue that major platforms like Twitter are essential to free speech, maybe even persuasively. What you can't do is make your case as if it were a self-evident fact. It is not.