It was not just the demotion and reduction in pay that was distracting him. It was the future direction of his career and life, as dictated by a fairly contentious decision by the company. Look at his age.
Agreed he should have done better on the day. But, perhaps because of the above, he should not necessarily have been flying on that day. Try taking yourself off the roster for psychological reasons; those same reasons will prevent you doing so. It is at this point that a good management team should be intervening, for crew welfare as well as safety. So why did the management systems fail? (Money?)