Bit of a trick, going on here.. my initial thoughts were it was amazing and the 400 was generating the graphics in real time? Scanning over the details quickly during my lunch, it seems it is playing a video of the graphics from a cartridge "the!Cart". I guess it is impressive, but it's "just" a video stored on a rom cart?
The mere fact that the 400 can stream video of this quality is impressive, using The!Cart is really no different than streaming video from a hard drive or over the Internet. But I think it's more impressive that it's using the audio track on the Atari cassette and syncing it to the video at the same time! That audio isn't being streamed from cartridge, it's streaming from a streaming tape!