Around the same time, 460 men in 6 ships destroyed 30000 men in 400 ships taking over Ormuz. Portugal and Spain were just incredibly OP during that time period. And the people in Ormuz were more advanced than the natives in US. And they still got absolutely destroyed.
It seems like the Incans were overconfident and didn't expect a surprise attack (didn't have their weapons, only a small retinue around the rule in ceremonial garb instead of armor), and then the 8000 warriors were outside and didn't even attempt to fight the Spaniards because they were so demoralized.
Ah weird - the text of the page says Atahualpa had 80k troops, but then the infobox describes the Inca forces as 3-8k in size. I guess not all the 80k were involved in the battle
Disease was important but there was a large technological and cultural gap too (e.g. the Incan didn't fight at night!).