At the bottom of the page where the video is it says:
Second, while these stories are not written by J. K. Rowling (obviously) they, and other such stories, have been sanctioned by her, so long as they are respectful and appropriate for children. I have been in contact with Ms. Rowling's literary agency (after they were asked by the press if the James Potter stories and websites were secretly her creation). They have been very cordial and encouraging, even going so far as to actively deny erroneous press allegations that Ms. Rowling intended to sue me. For that, I thank them!
I don't know how true this is, I imagine it's probably true. So I don't think he has anything to worry about as long as he doesn't publish the stories or earn any money off of them.
I applaud this guy, he really has worked hard. I didn't read any of it, but it looks like he went through great lengths and created a really good fanfic. It's cool.