Majority shareholders may have some fiduciary responsibility to minority shareholders, so you might be able to make the argument that the board as a whole shouldn’t write disparaging remarks about the company. But even that argument is tenuous.
Her only personal fiduciary responsibility is to the mission defined in that collection of words, not to the employees of the for-profit.
That’s how this works whether you think it should or not.
You implied that she couldn't publicly disparage the for-profit because the board has a fiduciary responsibility to the minority investors in the the for-profit. I only piped up to correct that single point because it's wrong.
And that responsibility is defined as a fiduciary duty to the mission of the organization as defined in the charter.
As a fellow board member, if Sam thinks Helen's behavior is in conflict with the mission of OpenAI as defined in the charter, he is free to push for her removal.
Even in a nonprofit, the board has an obligation to maintain a good working relationship with their organization. It's very rare for a board member to publicly criticized for their own organization.
Also, this argument goes out the window because OpenAI is not just a nonprofit. When they started their for-profit subsidiary in 2019, they accepted a fiduciary duty to their investors.