Seems excessively harsh, I suppose German museums are serious business.
It did say at the end that a similar incident occurred several weeks before at the Bundeskunsthalle in Bonn, Germany, where a student hung one of her paintings on an exhibition wall and this museum, however, reacted more humorously. They twitted: “We think it’s funny & would like to get to know the artist. So get in touch! There will be no trouble. Word of honor.”