Agreed.
I carry the personal view that when someone says "text editor" they are implicitly implying plain text. As such the leading paragraph of the article makes me twinge a little when "text editor" is used rather than "word processor".
The article then continues on to describe the editor which sounds very much like a WYSIWYG editor. Indeed ProseMirror[1] homepage says the following.
ProseMirror tries to bridge the gap between Markdown text editing and
classical WYSIWYG editors.
It does this by implementing a WYSIWYG-style editing interface for
documents more constrained and structured than plain HTML
So whilst I've made a point of it reading oddly (and I would have thought this would also be the view of most others on HN) I am not trying to disparage the authors use of the term "text editor". But rather I am curious as to why such nomenclature happened to be used here as I seldom see it outside of descriptions of things such as Vim and Emacs.
[1] http://prosemirror.net/