It looks like there is a JSON[1] mapping OSM (id's?) to textures[2] and a .bis file which I believe is a 3D model format.

This is super impressive. I've been working on shademap.app for the past few years and they've implemented it's main functionality as an afterthought.

[1] https://models.f4map.com/cacheForever/24b0c4ec554a244c253e6a...

[2] https://models.f4map.com/cacheForever/e9e7a1217400e3fae1e56e...