> I think the coup is on the part of other employees who advocated for the board to fire Altman. No judgement in whether that was justified or not.
The GP was pretty clear that he thought "the entire board decided to do a coup," which does not fit that interpretation.
But even the scenario you describe isn't something that can be properly described as a "coup." In that case, the employees are just appealing to a legitimate higher authority, which is a totally OK thing to do (e.g. it's not wrong to report a bribe-taking boss to the company ethics hotline). IMHO, a coup is where subordinates illegitimately usurp and depose the highest authority from below.