The book will be written before he feels his work is done on FAI.

You know it's true because intuitively you need a non-work outlet for creativity and flow, and it makes sense to write about rationality in an entertaining way and to write a character (Harry) which he can take as an inspiration.

Of course, you also know it's false because the man prioritizes and FAI matters far more.

... I find a lot of rationalizations are like that. One of the most useful quick-n-dirty rationality heuristics LessWrong has given me is to 'consider the opposite'