What is most likely is that not every who lived in the land of moab was an offspring of Moab, just like not everyone who lived in Canaan was anything. After the Israelites took the land, it clearly states they didn't kill everyone and lived with them. What is moat likely is not that ruth lies, but that you interpret it to mean something it isnt. I dont see wyats hard about not thinking David had the blood of people God cursed to hell.