The Times article was the last straw, you know the board members all read that. Plus the space launch failure.
They sure look being a 'reliable' and 'competent' gang now.
Most likely some PR firm working for Boeing fed some hints to the the Times.
Boeing then waited until it was released to have a coordinated PR push and put as much blame as possible on Muilenburg.
And the board looks horrible, slow to act, behind the curve, reacting to external pressure instead of leading. So it would not be in the board's interest to do a "coordinated PR push" and fire Muilenburg after the stories were published.