Yeah, the linked article is very shallow. Heise [0] goes a bit more into detail, sadly the actual ruling isn't available yet.
Quick Summary from the Heise article: Axel Springer tried to claim that the website itself is a copyrighted work and therefore an adblocker would not be allowed to modify it. However the court decided:
1) Removing elements (ads) from being displayed does not modify the originally transferred HTML, but only the data structures as generated by the browser, which is allowed to be modified by the user. Otherwise using a browser without images would also be in breach of copyright.
2) The website in itself is not a copyrighted work, as there's no original creative effort involved in generating the HTML.
Quick Summary from the Heise article: Axel Springer tried to claim that the website itself is a copyrighted work and therefore an adblocker would not be allowed to modify it. However the court decided:
1) Removing elements (ads) from being displayed does not modify the originally transferred HTML, but only the data structures as generated by the browser, which is allowed to be modified by the user. Otherwise using a browser without images would also be in breach of copyright.
2) The website in itself is not a copyrighted work, as there's no original creative effort involved in generating the HTML.
[0] (in German) https://www.heise.de/news/Landgericht-Hamburg-Adblocker-vers...