Had you read the article, you'd have noticed that this exact fact is noted and asserted to support the hypothesis:
> And then there is the case of the Incas, who oversaw an empire that grew both grain and potatoes. The Incas developed a way of freeze-drying potatoes by leaving them out at high elevations. This technology allowed them to treat potatoes like a grain: non-perishable, transportable and taxable.
The inca was only one of the major pre-modern root-growing groups, and the only one which had access to freeze-drying conditions.
> And then there is the case of the Incas, who oversaw an empire that grew both grain and potatoes. The Incas developed a way of freeze-drying potatoes by leaving them out at high elevations. This technology allowed them to treat potatoes like a grain: non-perishable, transportable and taxable.
The inca was only one of the major pre-modern root-growing groups, and the only one which had access to freeze-drying conditions.