I assume that you are asking about the chapter by David Cahill in the book Questioning Collapse, edited by Patricia McAnany and Norman Yoffee. In this chapter, Cahill takes issue with some of Jared Diamond’s conclusions from his books. One of the statements that Diamond makes and that Cahill disputes is the idea that Huayna Capac died of smallpox.
To Diamond, the death of Huayna Capac from smallpox was one of the pieces of evidence (though by no means the only such piece) that showed the importance of “germs” for the European dominance of the world. Cahill disputes the idea that the Inca emperor could have been killed by this disease. He offers two reasons for this conclusion.
First, Cahill says that the word “viruelas” is not used until 1549. He implies that, if the emperor and a large number of Incas had been killed by smallpox around 1525, the word would have come into common use long before 1549. The second argument that Cahill advances is that there is no mention of the presence of smallpox in Cajamarca in 1532. If smallpox really had been introduced, causing a virgin field epidemic, there would surely have been mentions of the disease.
For these reasons, Cahill doubts that a European disease killed Huayna Capac.