Of course D&D is not an accurate picture of the medieval era. There's magic in D&D! There was not magic in the medieval era. What are we even doing here?
The author's point is that it's not like that. It's a persistent capitalistic medieval themed wild west with no real power structures. The feudal power structures were a defining feature of the european medieval era.
Of course it's fantasy and can be anything. The author is simply explaining that it says that it's theme is the european medieval era, while it has almost none of it's defining features.
I don't think that's what being stated in TFA. The argument is that there's nothing medieval about it (except maybe some of the weapons), contradicting Gygax's own assertions:
> You can be forgiven for thinking that OD&D is a medieval European fantasy game. After all, Gary Gygax himself says so. He describes the original D&D books as “Rules for Fantastic Medieval War Games” (on the cover) and “rules [for] designing your own fantastic-medieval campaign” (in the introduction).
As for this:
> There's magic in D&D!
You could devise a medieval society where magic exists. This is not what D&D does. That's the point.