Slidin Fast,
That's an interesting verse.
If an apostate is to be given death sentence, it is easy to see how such a law arose. See what the verse says why: "Stone them to death, because they tried to turn you away from the Lord your God, who brought you out of Egypt, out of the land of slavery." (Deut 13:10)
The very linking of the law with God's miraculous saving of Israelites from Egypt shows that this law originated from mere human minds because the story of parting of Red Sea itself originated from human minds, not a historical event. Story does not meet the standard of realism because after seeing such a great miracle no one would turn into calf worship telling one single calf "you are our gods who saved us from Egypt." (Ex 32:4,8,31)