What I remember is that their criteria to choose who were they throwing to the volcano was very varied and nonsensical. Like "children with more than one hair swirl" (not sure about last word, hope it is clear).

And sometimes they didn't use a volcano but just remove the skin of victimes and store them in a cave. They will use the skins to dress up and dance a month later.

In any case, victims were members of their society. It was maybe an honor. Yeah, colonizers were brutal, but it seems it was the state of the art back then...