I'd question how conclusions are being drawn here. I think the key takeaway is that output did not change. The authors then go on to say that since hours worked increased, productivity decreased. But how do we define what an "hour worked" really means? I know that I definitely spend more time "working" during WFH in the sense that I am either being responsive to colleagues or actively working on my own work. However…
I do think things would trend even more positively had this not been a pandemic. Folks would have more flexibility in work location and could "pick their spots" better in the sense that they'd have more control over their environment and could tailor it to specific tasks.