That's not exactly true, as Musk's offer is to buy the company outright, making it private (and thus buying out all shareholders), as I understand - so there is no concept of how Musk's ownership would affect the stock price. Still, the board can easily argue "we believe shareholders will be able to achieve higher profits in the future by maintaining their ownership than by selling all stock at Musk's offered price today".
He claims that he wants to “retain as many shareholders as is allowed by the law” [0] which is just as fictional as it was when he pretended to try to take Telsa private.
