By owning billions of dollars of Tesla, he probably deserves to be heard. And what he wants to say is simple and sensible: Elon is very distracted and Tesla deserves a full-time CEO.
Either that or Tesla has some skeletons in the closet that Musk knows about that haven't made it to the public yet. When the CEO of a company starts selling very large blocks of stock that is always a time to watch out and this whole Twitter saga started as just that, a pretext to sell a pile of Tesla stock.