I believe 40 just means “a lot” in ancient cultures in that area. Hence wandering the desert for 40 years, or sitting on Mt. Sinai for 40 days. The “great flood” has 40 days of rain. I think Gilgamesh has a 40 day journey someplace? Anyways, if there are any historical echoes in that tale, perhaps they just wandered the desert for a long time. Now I’m off to eat 40 Doritos…