How was this building made?

So I've been looking at micro cities the last few days because I want to get some ideas for building my own. I came across this build and couldn't seem to understand how it's held together? (specific questions at the end) Something has to be going on inside but I can't figure out what. Tried recreating it myself just to figure it out, but I've tried bars and clips, other SNOT bricks, brackets, nothing seems to be the answer. I also tried searching the image and it has been used in so many...