The answer to this can be found in Chapter 12. Specifically, it can be found on pages 224 and 225 in the paperback edition of the book. On these pages, Diamond talks about ways in which technology can spread from one place to another. He says that
Such transmission of inventions assumes a whole spectrum of forms.
As with any spectrum, there are two extreme ends for this one. At one end is what Diamond calls “blueprint copying” while at the other end is “idea diffusion.”
Blueprint copying comes about when one society simply takes a new technology and copies it. For example, imagine that you are living a long time ago and someone happens to travel through your territory with a bow and arrows. You have never seen them before. You ask that person to show you exactly how to make them and you end up making copies of that person’s weapons.
Idea diffusion is much different. There, all you get is the idea and then you have to work out the details on your own. In this case, imagine someone has been travelling and has seen bows and arrows. They come back and say “I saw these people using bent sticks with strings on them to shoot other sticks a really long way.” You realize that this would be a good way to hunt or fight and so you begin to figure out how to make those weapons on your own.
Thus, “inventions” come about in different ways. In some cases, the entire invention is simply copied while in others, only the idea is copied.