A good analogy would be using myths to predict the start/seasons or religious moral propositions. People 5000 years ago didn't know why not to eat pork etc. The priests probably made a connection to people getting sick and, because he didn't know they could just cook it longer, claimed God wanted it to be forbidden. Even in modern times the majority of people don't get why not stealing has real world value outside of God telling them not to. I'd argue that most rules of religion came about in this matter. In many cases the priest probably knew the real reason for the morals just like mathematicians know the real reason for the magical equations.

EDIT: I'm downvoting myself because I don't like my use of "real" in this comment.