Dark patterns are tricks, like making you click on something that you thought did one thing but does something else. Asking you to sign in/up is hardly a dark pattern.

And I've yet to see Medium "fill the screen" with annoying banners. In fact, from what I've just seen, Medium just displayed a web page with the article's bottom half telling you you've read all of your free articles and asking you to sign up.

Too much hyperbole on the internet these days...