Chapter 3 - And what about the "River Boy"?

After reading chapter 3, I asked myself what is actually about the title of the novel "River Boy". Until now, there was no "boy" mentioned in the book and I'm also very sure that the main actor of the novel is Jess, a girl. So what can I guess about a "River Boy"?
One can argue the river boy is already mentioned in the first chapter. Yet the recent picture of the grandfather is called "River Boy". Probably it will belong to the role of the river boy in this book, but I'm convinced that the whole book won't only concentrate on this mysterious picture which even doesn't have a boy in it yet. To my mind there must be a real boy as a person, as a character in the plot of the novel.
Nevertheless, it's my only ability to guess who could be this mysterious river boy and to ask myself whether the boy is mentioned somehow. People may say in my situation that the river boy is not mentioned, but there is either no indication for that.
So I'll guess who of the mentioned persons offers the ability to be the river boy. I think the river dealing with the river boy is mentioned yet. It seems to be the river beside the holiday cottage of the family because it's described so detailed (the whole third chapter describes the river in actual). And why would the author let the family go for holidays to a remote place that only the painter of the picture "River Boy" knows and where he lives in his childhood otherwise?
So at my point of view, no one of the family never being at this river before could be the river boy, except grandpa.
He may be the mysterious river boy of his picture and I think that is one rational possibility. Grandpa is going to die and had a cruel childhood at the place where the river is located. Both of his parents died and it seems as his childhood was always a demonstration of weakness for him. So it may be that Jess' granddad wants to tell his family in this picture something about his past he never had shown them before. Perhaps he also wants to remind himself of those experiences he made with the river when he was a little boy, a river boy. That could also be the reason why he wanted to travel with them to that remote place of the river.
However, I have also another imagery of who could be the river boy. For me it is also a possibility that Alfred that mysterious guy grandpa talks about at Chapter 2 could be the river boy. Alfred, that's what we already know, will be, if he's still alive, in the same age as grandpa. So he won't probably indicate a boy yet, however it is possible that grandpa wants to draw a good friend of old times in this "River Boy" picture.
I also would conclude coherence between the end of Chapter 3 and the river boy. Jess feels observed herself by someone, but she cannot guess who is it because she sees nobody. Perhaps the river boy, Alfred, observed her while swimming.
All these specs needn't to be right, but both of them are coherent to the part of the book I read. So they might be fortunetly right.