The author mentions one of his respondents who wrote that he got most of the meaning in his life from his job ... This led me to think about where I derive the meaning from ... Definitely not only from job. Job is a process after all, I think the meaning could be rather attributed to the results of it.
But the issue is that many people may not see direct results of what they do at work, so they attribute the meaning to the job itself. And if they are offered 2-3-day work week, they might feel like they would be losing the meaning in their life.
I heard this argument from other sources too that people would get depressed when not busy with work most of their life. I doubt that, at least less people would get depressed from getting more personal time than are depressed now from the necessity to spend most of their lives at work which is also rarely truly enjoyable.