The reason it looks photoshopped to me is that the rock is far too bright for the time of day indicated by the sunset-clouds above. Idunno, maybe Blitzo just has one big mother of a flash on his camera. But the contrast between the edge of the rock and the sky doesn't look natural, nor does the angle of the clouds compared to the angle of the rock. It just doesn't jive. Then again, Blitzo isn't one to post cheap PS shots on this site, so maybe its real and it just looks uncanny. Blitzo? What say you?
The easy way to Photoshop it would be to remove the original sky and replace with the sunset from another photo. I agree, the lighting does seem unnatural. It's a low-light photo, though, hard to say if it is a merged shot or not.