The ruling, and indeed this thread, is not so much about who was at fault at causing that sad accident. The events have been covered extensively elsewhere on PPRuNe.
The court ruling is about who can legally control airspace in Germany. It is the courtīs understanding that the German state, represented by its government, was not in a position to "outsource" ATC to a Swiss, and private, firm because this was a breach of its constitutional liability.