I read this elsewhere, and it said that if the Germans wanted to make a public things for internal consumption they would have sent some low level people packing. They would have made a point, and then expected everyone to believe that the matter was dealt with.
However, this person is the liaison person in all the public and secret co-operation projects between the Germans and the US. So, sending him home throws a spanner in the works of all levels of co-operation - not least the intelligence sharing. So, yeah, the Germans aren’t screwing around.
Maybe that’s something Cameron should think about after the less than stellar performance during the EU summit in Ypres earlier.