I'm telling you, the background wall of trees, the tree at right at the middle distance in the beam of light, the island of trees, the boat....those are all completely separate photos composited and blended beautifully.
have a look at this tutorial: http://photoshoptutorials.ws/photoshop-tutorials/photo-manipulation/create-this-breathtaking-photo-manipulation-of-a-tightrope-dancer-in-photoshop/
You could well be right, it may be a composite, the file is way too small to scrutinise it. The shadows, or rather lack of them, ring alarm bells. Also the light is showing a lot of air diffusion in the background, but the air between the photographer and the boat is very clear. However a telephoto could create that effect, I've had it myself.
Either way, at this size of image it looks very well done, and is a beautiful picture.