If it was able to detect roughly how many buildings there are in that area, that’s already fairly useful at global scale. It seems they are focused on measuring urbanization. It’s good to know though that it may be dodgy at that level of granularity.

Indeed, my neighborhood doesn't show any buildings at all even though I know all of our houses have been there at least 30 years and were still there when I left this morning.

I haven't visited the map, but I wouldn't be surprised to learn they didn't attempt to re-create the building shapes, just location and estimated size. The real shape seems pointless for this dataset.