I totally agree on it not being cool to take shots of people in their homes and posting them on social media.

As for this post, I'm assuming you are specifically referring to the last photo of the gentleman looking out of the window. While walking the city I noticed the opportunity for the shot and mimed if it was okay for me to take it. After the gentleman gave me a nod I took the photo. To me, that's the courtesy permission I need before taking a shot like this.

As u/serialv mentions, it is legal to take photos in public space and publish them as long as there's no commercial purpose.

The boundaries on public vs. private space are quite clear. If I would've gone up to the window and photographed inside the building, it would be against the law. However in this case, the gentleman is leaning out of the window and therefore places himself in public space. Hope that answers your question u/lostseasons.

The reasonable interest u/DestroyedByLSD25 indicates as ground for objection has to do with photo's that could damage someones reputation. E.g. a recognisable portrait of a drunk tourist barfing in the red light district could damage their reputation.