They are just ordinary hikers who happened to be in the right (or wrong, depending on how you look at it) place at the right time. They could be nature lovers who enjoy exploring the outdoors regularly.
I'm not sure of the exact details of their story. Maybe they were out on a normal hike and stumbled upon him in an unexpected place. It could be that they were in a remote area and noticed something unusual which led them to find Sands.
Julian Barnes' novels often have a strong focus on human nature. For example, in 'The Sense of an Ending', we see how the main character's self - perception and understanding of his relationships are deeply intertwined with his sense of self. His works also tend to be very cerebral, making the reader think about complex ideas like truth and memory.
I don't know who the author of the 'julian novel' is. There could be many people named Julian who could potentially be the author, or it could be a pen name.
I'm not sure specifically what a 'julian novel' is as the term is rather general. It could be a novel written by someone named Julian, or it could be a novel with 'Julian' as a main character. Without more context, it's hard to say.