Actually, I am inclined to believe them due to one very important reason.
For the past few days, we have been under a major hack attempt as well. Luckily our host has pretty good security but we've been banning IP addresses and increasing security thresholds on our part. I also heard another major political forum that most of us are familiar with, has been also undergoing a similar intrusion.
Something seems to be targeting political forums, left and right. I think the video and stuff left on DU as a type of vandalism, wasn't really done because they were from the left but just as vandalism, maybe to make them think it was politically motivated.