That makes the article extremely silly, actually almost pointless.

If you don't see difference between plain text files and text files then that's pretty much it for this conversation.

EDIT: just to hammer this point home; if you gave me a task to write a report in plain text and I delivered a .txt file with some custom markup language, would you consider the task to be completed satisfactorily? I wouldn't. You can argue that the specification of the task didn't exclude custom markup language, but any sane person would understand what plain text file means.