The SoBufferedShape node uses SoBufferObject which contains the actual data of the geometry. Using this buffers it calls fast OpenGL rendering functions. In order to avoid BoundingBox computation which can have a huge cost specialy with SoGpuBufferObject in animated environment the demo uses a SoBBox with a user defined bouding box. As long as we compute the vertices, computing the actual bounding box is straightforward.
SoBufferedShape, SoBBox, SoBufferObject