It seems as if the Church wants to leave the Book of Mormon in a sort of gray area where it may not be 100% historical. Nelson's remarks are confusing as the Church, since its foundation in 1830, has always said the Book of Mormon is a true record of the ancient inhabitants of the Americas. The remarks appear to be geared to the complete and utter lack of any archeological, linguistic or any of scientific evidence to support it. To the contrary, many anachronisms are mentioned in the BofM such as horses, elephants, wheat, barley, steel, silk, etc. which did not exist in the Americas during BofM times. Elder Nelson seems to want to lessen the validity of these arguments with his dismissal of the BofM as a 'textbook'.