Considering the person is saying how bad it is to have a tracking pixel in email, the site that hoats this article can now do similar things by putting that cookie in your browser
<script>document.cookie="resolution="+Math.max(screen.width,screen.height)+("devicePixelRatio" in window ? ","+devicePixelRatio : ",1")+"; path=/";</script>
In fact, that's pretty much what it is. This looks like it comes from an older version of the Adaptive Images WordPress plugin: https://wordpress.org/plugins/adaptive-images/ (there's a very similar version of this code in the adaptive-images-front.php file).
The WordPress install would use this cookie to resize an image to send to your browser.
Could that itself be used for tracking? Sure, but you'd need at least a few other signals as screen size and DPR aren't all that unique across most devices.