My guess is that they experienced something like this and needed larger sized normal shoes to accommodate the more natural foot shape.
https://www.reddit.com/r/BarefootRunning/comments/1ec5i5n/di...
https://www.reddit.com/r/BarefootRunning/comments/1ec5i5n/di...
It's kinda like how some nicer brands offer a variety of size modifiers in addition to "small, medium, large" on their ready-to-wear shirts, like "slim", or Brooks Brothers' named fit-variants ("Regent", "Madison", et c)