Of course we can only theorize about this, but from a developer's perspective, think about the beginning of HTML: Most (if not all) menus were tables, even though they had to be
UL (as they're now). Circular or radial shapes didn't exist other than as images. I think linear build was a consequence of that limitation.
Now, after decades of using linearity, most people understands the behavior of a menu at simple sight. If you used a XEROX machine, you'd realize not even them are using a radial menu, so I'm quite sure the results wouldn't be the same nowadays.
Personally, I tried doing something like this based on circular navigation tutorial for a project, and I've found the results were quite poor. Tests shown that everybody liked it from an aesthetics point of view, but everybody was really confused. And keep in mind we were using only one level, unlike the (really interesting) video which has several levels, so we ditched it. Therefore, I have to assume that people understands the affordance a linear menu transmits