we get asked to make composite shots for advertising campaigns and if you were asked to recreate that shot it would be so tricky. you would need someone to have posed on say, a barrel, the exact same height as the horse, and turned at exactly the same angle (which would be really tricky unless you were measuring it and setting it up purposely) and photographed with the same perspective as the original shot. his body is lined up perfectly with the line of the horses body.
you couldn't have clipped his body off a shot of him sitting on a horse, because his weight is in his left foot, so it isn't dangling like it would be on a horse. the way his leg is curved around the horses body is 100% correct and that would be tricky to do.