The answer to this question can be found beginning on p. 252 in the paperback edition of Guns, Germs, and Steel. These three societies, Diamond says, were all indigenous societies that were more interested than others in adapting the ways of the Europeans.
These three societies were from very different areas. The Chimbu were a tribe in the eastern highlands of New Guinea. The Ibo were from what is now Niberia. The Navajo live in the Southwestern United States. Though far from one another, these groups all adapted readily to European technology.
One of the main points Diamond is trying to make in this chapter is that people from all continents have an equal chance of being interested in adapting technology. There is nothing about Native American culture, for example, that makes them averse to borrowing technology. Some people say that there are such differences and they claim that the peoples of some continents are culturally backward and do not want to borrow technology. Diamond claims this is false. He uses the example of the Chimbu, the Ibo, and the Navajo to show that there are indigenous people on all continents who are willing to adopt outside technologies.