Kdawg explained that this experiment uses an interior-mapping-style technique, allowing them to generate a 150x150-unit city filled with these buildings. They don't plan to release it as a purchasable asset at the moment, but you can still take a look at what's happening behind those windows:
You can also find more of Kdawg's procedural city below and follow them on Reddit for updates:
We've covered other interior mapping-based experiments on 80 Level before, like this impressive cube by ごんびぃ: