They are likely to be using kit like this:
www.cameras4sports.co.uk/product.asp?id=134Small lipstick (helmet) cams that can be strung between the lines of the kite and pointed down towards the rider.
You can get them in all different flavours, including a wireless, so they transmit the signal to a video recorder on the beach or there's some that record directly to SD cards in the camera unit itself.
The fixed shot of the rider staying stationary whilst the horizon moves can be done in realtime (no software needed) by fixing a harness/brace to the rider and attaching the camera to that.