@durchaus That's a very interesting interpretation and twist.
But changes on client-side is not a modification of their code. Their code remains intact, so there's no Copyright infringement.
What they're claiming is no different from saying that writing on a book or any modification on the book is Copyright infringement because you changed your copy of the book. How can it be when you did not violate the Economic Rights of the Publisher and the Moral Rights of the human authors?
It's the same with code residing client-side, it's just a copy so the browser can display the site. Whatever happens client-side is only available for that client. No Economic Rights of the Publisher was violated. No Moral Rights of the human authors were violated.
They're twisting things. But I do see how they're trying to play it. The problem here is that, if the judges don't understand the techie side, they'll easily believe their code was modified which everyone can then see, when in reality, it only happened client-side.