Earlier quoted context omitted.
I think this was a polite way of saying they couldn't agree on terms of his board position. For example, he would probably have been restricted on the kinds of tweets he could make. He recently started a poll asking if he should turn Twitter HQ into a homeless shelter because so few people show up. They would certainly not want him doing that if he's on the board.
There is no agreement on terms. As a member of the board you are required by law to always do and say what is in the best interests of the company and its shareholders. Someone probably sat him down and explained that he doesn't hold a majority of voting shares at Twitter, and that the company and other investors wouldn't put up with his shit. With a 75% majority, the other shareholders could vote to nullify his shar…
The SEC would be extremely interested in such an attempt.