JK's right. The video camera he's using has a rather wide lens, which makes the path look narrower than it is. Still, they'd better be dang careful! Snagging a handlebar on the cliff might toss you over the edge.
Geo, so the camera adds more weight space? Even still. I saw a vid of dudes doing similar trail on mountain bikes, and one dude lost his footing and went down to his death. Looks fun, but I don't feel like going out like that.