The Poison Pill plan was from the Board, to stop Musk from following through with a hostile takeover. But Elon reportedly convinced numerous large shareholders of his plan[1]. Even if the Board isn't a fan of it, the Board of a publicly traded company is ultimately beholden to their shareholders, so if the shareholders are convinced, they need to consider it.

1. https://www.reuters.com/business/exclusive-twitter-under-sha...