We say this all the time but act as if it's some secret, or just a cynical remark, but it's not either of these. As a general rule your boss likes that you can feel their perpetual gaze as you work, even if in practice it means you are working less.
Because of course you aren't working all the time, and of course you are not 100% being productive. Everyone knows this. It is not a secret that even the most productive engineer spends a huge amount of office time doing nothing.
No worker (as I general rule, I know there are exceptions) prefers open offices to either cubicles or real offices (I wonder how many HN have ever had these?). Nobody feels that they work their best when someone is watching them. Everyone knows that part of working in an open office is figuring out how to create the illusion that you are working.
The only reason to have an open office is because the people making the decision for how the office should be, and the people reporting to them, do in fact like to watch you work, because they like the control that they feel when they do this.
Please let's stop pretending that we don't all understand exactly what open offices are about.