I'm skeptical. Hard to explain why, just a feeling. Not enough technical details to explain how this is supposedly being done. The entire video has a hoaxy feeling to it.
I'd love to be proven wrong, if anyone has related info.
I think that the audio/music from the iPhone is passed to airplay which is triggered by sending commands to Siri, then via the airport express is connected to a device created by Yamaha to then convert the song to play on the piano.
I'd love to be proven wrong, if anyone has related info.