Does a board give an assignment to the CEO or teams?
If the case is that the will of the board is not being fulfilled, then the reasoning is simple. The CEO was told to do something and he has not done it. So, he is ousted. Plain and simple.
This talk about projects given to two teams and what not is nonsense. The board should care if its work is done, not how the work is done. That is the job of the CEO.