Actually flying the a/c is pretty stress free for those who know what they are doing. The received stress is a byproduct of other factors, ie staggeringly long or multiple sectors at appalling times after little rest in a noisy hotel, constant disruptive roster changes, concern over whether you will pass your next medical, hassles with security, the precarious financial state of the company, etc, etc.
I’m sure many actual pilots here can add to that list.
These are not transient problems. These are stress factors not common to all jobs.
Perhaps this is what influenced this survey, not that I agree with it.