When asked to comment on the book, Cook should have said, 'I haven't read it.'
The book is crap.
The reviewers know it's crap.
The author knows it's crap; her objective is to keep people talking about it for as long as she can.
I don't think Tim was as concerned by his portrayal; he was probably incensed by the portrayal of Apple's employees, and while his instinct to stand up for his staff is admirable, I think this was a poor response.