How I understood it, the name refers this NIPS 2016 paper (http://carlvondrick.com/tinyvideo/) in which video-generation happens in a two-stream architecture; therefore, relying on a static background. The approach posted here is generating videos in a single stream from what I see. Therefore it does not rely on such assumptions. This is possible by their architecture, on the one hand, and optimization within the WGAN framework on the the other hand. The dropped assumption on the background also allows using the architecture for different applications if you look at their homepage.