Reading a book about a place is not reasonable grounds for suspicion.

To all the people saying we need to be cautious because of all the incidents lately, there is factually more of a risk of getting into a car accident than there is of being a victim of a terrorist attack. Should a police officer pull someone over for suspicion of drunk driving if they see them get into the car carrying a book about vineyards? If not then how is this appropriate?

Of course we should take reasonable precautions against terrorism just as we should any threat to public safety. However, that does not mean we should jettison reason and accept every reported fear as being reasonable. Should the flight intendent have reported it? Sure, anyone who thinks they saw something suspicious should. But it is the responsibility of the authorities to evaluate these concerns and determine whether the reports they receive actually reflect something that could reasonably be taken to indicate terrorist or other criminal activity. Reading a book is NOT one of them. Sometimes you have to tell a person "thank you for bringing this to our attention but we do not believe that this indicates a problem."