Exactly this, why the "pure" label when obviously not? The main reason for me to click through to this thing was exactly that; I love seeing people push an individual tech like CSS on its own: there's nothing tech-wise news worthy in oldschool js/css solution like this.
I don't think that level of cynicism is warranted: the individual mice are, in fact, styled via pure CSS. The small amount of JavaScript that's used is a convenience method to toggle which mouse is visible[1], and the work that was done here does not change in any substantive manner without it. If all the mice were displayed simultaneously side-by-side it'd be equally impressive.
I'd wager most of us are happy with the concept that it's being presented on CodePen with a bit of helper JS so that the target audience (developers who are unlikely to disable JS, or are happy to enable it for a site like CodePen) can better appreciate the demo.
