Edited later to add:
The original press release seems to be gone now, but here is what is claimed to be the revised release, and an article on the same topic.
https://www1.wdr.de/nachrichten/polizei-dortmund-greta-gewaltbereit-100.html
https://www.yahoo.com/news/german-politician-calls-greta-thunberg-102611513.html
German here: if you take peaceful demonstration as an option away from people, they are left with two options: being resigned or non-peaceful demonstration. The German stance to hinder peaceful demonstration against the Israeli atrocities is stupid and labeling Greta Thunberg as primed for violence is beyond stupid. And the majority of Germans has no active memory of the 72 Olympics incident.