I need you to write something down, he said. It was, he said, for his new book,...

I need you to write something down, he said. It was, he said, for his new book, not for mine, a point he stressed because I was at the time researching a book that involved sports...When I gave him the note the next day he said "You can use it if you want to." What did he mean?
Did he know he would not write the book?
Did he have some apprehension, a shadow? Why had he forgotten to bring note cards to dinner that night? Had he not warned me that the ability to make a note when something came to mind was the difference between being able to write and not being to write?