That's less fiduciary duty and more hacking a payday.
A large golden parachute for firing a board member could be a disincentive mechanism to do it: a 'poison pill' of a kind.
* https://en.wikipedia.org/wiki/Shareholder_rights_plan
They could have felt they were doing the right thing, and making a public statement of the situation, but knew it was a bit of a kamikaze tactic and so made it more painful for when the eventual backlash occurs.
If they truly believe the CEO was destroying the company/its value.
> Special meetings of the stockholders may be called by the board of directors or by such person or persons as may be authorized by the certificate of incorporation or by the bylaws.
California law specifically allows for a meeting called by stockholders with 10% of the vote, but for Deleware, a large holder would need authorization in the bylaws. If there was no such provision, a board could plausibly control the company until the next annual meeting, or until court action. Annual meetings can be delayed a bit, but any stockholder can force one once they're a little late.
If you were concerned about the judgement of the CEO/majority holder, and you were optimistic that it was a temporary issue, it might make sense to remove said person for as long as possible; be it a few months or a day and a half.
[1] https://law.justia.com/codes/delaware/title-8/chapter-1/subc...