Looks like they outsmarted themselves. They took a secondary route between oases to the south to avoid fighting Egyptian garrisons on the main route that historians were looking on. The Persians dug and lined with clay pots wells along the way. (The aquifer was not so deep 2500 years ago.) But when they arrived at what they thought was the oasis of the temple of Amon, it turned out to be another oasis 60 miles to the south of the right one. While they were trying to figure it out, the sandstorm hit.