Heh. Possibly they noticed that assorted queries all lead to the identical page content. If so, I agree that they deserve credit for recognizing that this is fundamentally a "soft 404" rather than Duplicate Content.
Maybe they would be happier if you tweaked your page-generating code to return a 404 response in situations that lead to the "Sorry, we don't have any articles" page. To the human user it will make no difference, since there's no inherent connection between the page they see and the response the browser receives.