What was going on: Herodotus has just said that Cambyses must have been insane to mock other peoples' religion and customs, since every people thinks its own customs are the best. As proof, he tells how King Darius asked some Greeks what price would make them eat their dead fathers, and they said no price would.
A people who ate their dead parents were horrified at the idea of burning them. Beliefs run that deep. Custom rules everyone, I think.
Then Darius summoned those Indians who are called Callatiae, who eat their parents, and asked them (the Greeks being present and understanding through interpreters what was said) what would make them willing to burn their fathers at death. The Indians cried aloud, that he should not speak of so horrid an act. So firmly rooted are these beliefs; and it is, I think, rightly said in Pindar's poem that custom is lord of all.