Well the story said that he might have done this as a young man. The works with which we are more familiar were done when he was older, so why couldn't his style have changed somewhat, and matured over the years?
I don't really have any good reason to doubt it , other than based upon my readings of his life and personal viewings of his works- it just doesn't feel right, to me.
But again- I think it would be an exciting story if I were wrong.