Actually I was incorrect about the details of the incident. It was even more totally uncalled for. The capt pressed EXPED Instead of APP by mistake passing 3600ft to target altitude of 3000ft. He didn't have to cancel it because ALT* engaged immediately and aircraft had levelled off. End of story. But he didn't check the FMA and tried to push EXPED again to cancel it and again by mistake pressed ATHR causing ATHR to go in THR LK. So? just re engage by pressing ATHR again. Again would have been end of story. Unless he went for AP switch this time. But since he had enough of the FCU, for no reason whatsoever went for the click, click. That was actually the blunder which could have killed everybody.