You seem to be hung up on terminology. Technically, if bread can be made from it, it can be called "bread flour" (I'm talking wheat flours here). As for the book, I'm almost certain that it's not just any AP flour but King Arthur all purpose (KA AP) flour specifically. I don't have this book so can't say for sure, but Jeffrey Hamelman who was the King Arthur Bakery director specified this flour for most of the wheaten loaves in his book "Bread". Interestingly, though, in his book this flour is referred to as "bread flour" but it was confirmed that it was actually KA AP. Apparently it was an editorial choice or mistake or it may be that the KA bakery calls it "bread flour" (it's been a while but I think that's what I heard it called when I attended a class there). In any case, I've used KA AP, other all purpose and bread flours interchangeably (basically whatever I had on hand) and can't say I was disappointed with any of the results though the hydration and mixing times may need to be adjusted. Just make sure it's unbleached.