When a thing turns habitual surely it'll kill time. One such thing had taken place with employee. It is not about gambling, as said whatever he had done apart from his assigned task during the work hours is going to stop his productivity as well as the progress of the firm. This is well understood by the Boss and he had fired the employee.
Yes, all bad habits that are done during working hours will indeed result in decrease in worker productivity, especially if it is gambling activity, they will not focus on what to do because an employee must really maintain professional attitude and of course it is their own risk when the leadership takes some harsh consequences to their work that makes mistakes.
But in context like this, no one will really know the truth except from the leader himself and his workers, anyone can lie.