[eiskalt]

No, all 3D buildings data is provided by OpenStreetMap. This wiki page describes the model:

http://wiki.openstreetmap.org/wiki/Simple_3D_buildings

In short, all complex buildings are defined via multiple simple polygons with height, height under ground, colors, etc.

For example, you can check how Saint Basils Cathedral is defined (take a look at Members list):

https://openstreetmap.org/relation/3224486