If I hire someone on a salary and expect him to do X, and he meets that expectation, I wouldn’t care if he did it in 40 hours or if he did it in 10 hours and spent the remaining 30 hours fishing. I hired him to do X and he did. Why should I care how many hours he’s staring at a screen?

Now if he’s on an hourly contract, I’d expect the hours to be accurate.

For some jobs the expectation is literally “be reachable and physically at this workstation when a fire ignites”. Can’t do that while fishing. But lots of jobs are “do this batch of things, and come to these meetings at these times.” If someone can do this effectively from the middle of a lake, who cares?