That's possible, but they wouldn't necessarily have opened with Teenage Riot, as it wasn't a DDN show.
The review clearly says he played along with them on stage, but then again the reviewer doesn't seem to be very knowledgable about the band, so I don't know. I'm sure people returning from the festival today will be able to tell us.
http://3voor12.vpro.nl/3voor12/festi...52 08&type=-1