From my understanding, the board has no (direct) say in this. He's asking the shareholders - i.e. anyone who owns Twitter stock - to sell to him for that price

From my understanding, the board has no (direct) say in this. He's asking the shareholders - i.e. anyone who owns Twitter stock - to sell to him for that price until he has the required majority. All the board can do is put up measures to make this hard (like the poison pill thing).