It's the standard playbook. By having the CEO leave it gives the impression that it was his decision and so the bad decision-making is gone and now the company can be trusted again. Of course it wasn't his decision; it was the whole board's, but it's convenient for them and their stock price to make it seem like it was his.

No way to know, I suppose, if it was him + the board vs everyone, or him vs the board... but unless somebody leaks the details, I'd assume the board is just as culpable.