Except for the fact that the book takes quotes from Lucas from back in the '70s. That was the whole novelty of these books, Lucasfilm allowed Rinzler to access notes and recordings that have been dormant in the archives for years. The Obi-Wan and Owen behavior when talking about Luke's father was due to the fact that they were talking about a grim subject and didn't know how to tell Luke that his father was betrayed and murdered by Vader. It just so happens that it works well with the retcon of Obi-Wan lying about it. And Gry, you're right, that quote was the closest I could find to confirmation, but after you read these books it becomes obvious that Lucas evolved the whole story of Star Wars over time, it started out as a very different thing. He never had the prequels figured out, just a small synopsis. He always just had little ideas that grew or morphed as he wrote, directed, and then edited together the movies.