While this is true, I strongly doubt OP is talking about this case. In your example although it did look like you didn't work from the outside, but in your mind

While this is true, I strongly doubt OP is talking about this case. In your example although it did look like you didn't work from the outside, but in your mind you were still thinking about the problem, technically speaking, working. The case in discussion is how we developers do just the bare minimum consciously (or unconsciously) and the fake away the rest. Even with this perspective I don't consider it wrong at all. Our developer brains can be in "the zone" for not more than 2-5 hours everyday. If we force ourselves to be in the zone more than that, we are just damaging our runway and heading towards a burnout. That said, the only thing we could do is - learn how to increase our zone hours. John carmack went to the extent of measuring his bathroom breaks as a way to extend these focus zones. While that is a bit extreme. generally as developers our antidote should be to optimize our focus zones to what fits us.