The Captain is in charge of the aircraft, period. He signed for it and it is his till he signs it back in. It's very important who said what to him, why they said it, and more importantly should they have said it. The Captain remained in command though and decided the situation demanded an evacuation which is exactly what he ordered.
Remember if he had taken the advice not to evacuate and the unthinkable had then occurred he would have been the one held ultimately responsible and you can bet your bottom dollar his employers would have held him responsible to.
Unless their are reasons we are not being told, which I highly doubt, sacking a man for carrying out his role as Captain is ridiculous. If there should not have been an evacuation that's for the FAA to investigate, advise on and apportion blame.
The whole thing smacks of double standards by the Airline.