This is legit like in any given neighbourhood in Germany you’ll see open windows. Doesn’t matter if it’s winter or summer. Sleeping with the window open isnormal. In the UK in the average neighbourhood, windows will be overwhelmingly closed. And they’re much smaller than in Germany anyway. In Germany, normally all windows open all the way (even the ones that are so high up that you need a ladder to open them). In the UK it’s not unusual that only part of the windows opens - a place I lived in had windows where only the upper fifth of each window would open - and you even have houses that have like four or five windows side by side and only the two outer windows or part of the two outer windows open. I also had to live with 5 people in a house share for a while and I was the only one who ever opened the kitchen window or the living room window, and even if the water from the cooking was streaming down the window pane there’d be an argument whether it was really necessary to open the window now.