Google has built their own vector map rendering engine based on OpenGL ES version 2: https://developers.google.com/maps/documentation/android/start#requiring_opengl_es_version_2
Here's a link about OpenGL ES on Android:
http://developer.android.com/training/graphics/opengl/index.html
OpenGL lets you leverage the underlying power of the GPU and get performance on par with 3D mobile game engines. Given the complexity of most high-end mobile games these days, rendering out some vector map tiles and 3D buildings seems like it would be on the low end of performance requirements.
This is why the requirement of the Maps API V2 is Android 2.2 and higher, since the OpenGL ES Android libraries also require Android 2.2 and higher.
As far as implementing your own version of this, I'd look into some general 3D rendering examples using OpenGL ES and available libraries for Android.
This SE post has some info: https://stackoverflow.com/questions/9450308/android-latest-open-source-3d-libraries-for-android
...and this: http://ntt.cc/2011/05/08/8-open-source-android-game-engines.html
I haven't seen any 3D OpenGL ES engines aimed at map rendering, but they might exist.
