Indeed, that's simple. It's either hyperbole at or extremist right wing propaganda or, if you know it better, a lie.
Die Linke -or to be precise Ulrich Wilken (Die Linke) deputy President of the Hessian Landtag- actually organized and officially registered the legal part of the demonstrations yesterday. Die Linke is closely knit with blockupy. However, as has been said by caratacus, such demonstrations always attract loonies who are ready to resort to violence from all kinds of backgrounds, especially from anarchist and extremist leftist groups not necessarily directly linked to Die Linke.
However, it was short sighted and naive not to expect such groups to be attracted by this demonstration. We've seen such things happen on multiple occasions across Europe since Genua '01. Hence why there was such a huge police presence in Frankfurt to begin with - it was to be expected to happen.
As for your question with regards to the reception in German media, here are some articles:
http://www.zeit.de/politik/deutschla...destag-debatte
http://www.zeit.de/politik/deutschla...test-kommentar
http://www.faz.net/aktuell/rhein-mai...-13492647.html
http://www.faz.net/aktuell/rhein-mai...-13490592.html
http://www.fr-online.de/blockupy-fra...,15402798.html
With regards to Die Linke and Russia, that's a very special relation rooted in the history of several predecessors of the conglomerate that made up the foundation of the party Die Linke (including the PDS/SED). Die Linke is usually very Russia-friendly, while not necessarily Putin-friendly.
That all being said, as a personal comment to what happened yesterday and the night before, I live in the greater Frankfurt area, reasonably far away from it so that I didn't see or hear anything personally, but three of my workers who partook in a professional development course in the city witnessed parts of what happened first hand and when I talked to them today they were disgusted and frightened by what they've seen yesterday. Of course, that's just anecdotal hear-say, but nevertheless.
All in all I think it was a despicable show of how people can exploit freedom of speech and freedom of demonstration. Resorting to violence makes them nothing but criminals and in the end, the average Joe has to pay for all that with his tax money.