Apparently it wasn't an isolated incident but a lot more widespread, also happening where German and French troops were facing each other. (The German author Carl Zuckmayer talks about it in his autobiography.)

At least three books have been written on it:

Stanley Weintraub, Silent Night: The Story of the World War I Christmas Truce (Simon & Schuster, NY 2001)
Michael Juergs, Der kleine Frieden im grossen Krieg (2003)
Malcolm Brown, Christmas Truce (????)