Yeah, they're just assuming that if you wanted to store something you'd store it at the bottom of the hill.

While I'm no archeologist/anthropologist, I have seen an ancient grainery near the green river in Utah. It was about an hour long very steep half hike half rock scramble to get up to the ledge where it was at.

So maybe ancient people had reasons to put storage sites in more difficult to access locations.

It’s actually pretty common to store food at higher elevations in the historical and archaeological record, including among the Incas (but mostly in qollqas). More wind at higher elevations means less moisture, which is the biggest factor in preservation. There are plenty of examples from every era, stretching from ancient Minoans to 20th century Berbers.