This does not look significantly better then e.g. cities skylines, especially since they neither zoomed in or out, always showing only a very limited frame
All 3 of the other commenters are replying without having done any actual thought or research. The paper repeatedly references MatrixCity and another commenter above found this https://city-super.github.io/matrixcity/ which also, I'd like to add, calls out that it's fully Synthetic. And, from what I understand, is extracted from Unreal Engine.
This is a 3D reconstruction, rather than a game rendering.
This was rendered from photographs, I believe
LOL this isn't a game engine, its real life photos being converted into gausian 3d views.
Actually it sounds like its from renders of an Unreal demo. So synthetic photos from a game engine. LOL