But he's acting as a board member firing the CEO because he arguably believes it's the right thing to do for the company. If he then changes his mind because the fired CEO continued a successful career then I'd say that decision was more on a personal level than for the wellbeing of the company.
His obligation as a member of the board is to safeguard AI, not OpenAI. That's why in the employee open letter they said, "the board said it'd be compliant with the mission to destroy the company." This is actually true.
It's absolutely believable that at first he thought the best way to safeguard AI was to get rid of the main advocate for profit-seeking at OpenAI, then when that person "fell upward" into a position where he'd have fewer constraints, to regret that decision.