Good answer, Bachus.

I'll just add that the title of the video is, "Introducing the Yamaha Montage Synthesizer" and then it shows the Montage being played throughout the video. Plus, it's from Yamaha Music London. To me, it's pretty clear the music was made with the Montage. I don't think Yamaha Music London would fool us. The sound is also in keeping with other demos.

However, anything is possible, I guess.

P.S. I actually tried out the Motif XF and other keyboards at the above store when I was visiting London in 2011. Nice store, helpful staff, and lots of Yamaha keyboards!