I thought my memory was failing me but I googled it and found this:
Scene illumination is a complex task requiring substantial processing power. Shapespark computes the lighting information only once, when the visualisation is first created. To save time the computation is automatically offloaded, using global illumination technology popular in state-of-the-art games to take advantage of cloud computing to do the hard work of rendering a requested scene as fast as it comes on the screen.
Has the plan changed? Shapespark seems to only allow local rendering as of now.