Ive heard of hin from other groups as well.
at first I also think it's fake but check out his other video
https://www.youtube.com/watch?v=DRWZldftsCA
https://www.youtube.com/watch?v=DRWZldftsCA

he practiced it well on his violin and of course, a violinist (and other classical fretless instrument) as used in playing the right notes without the aid of frets