Couple of issues here make this case interesting:
1) The 'security guards' were not paid, they were volunteers but still considered agents of the organization.
2) The 'compound' (more media nonsense really. I've been there [I'm not a Nazi, just wanted to check things out] and its not really a fortification on any level) has been shot at before. I know because I know the people who shot at it.
So here you have a couple of unfortunates whose car backfires in the wrong place, a couple of knucklehead 'guards' that think they're being shot at, and an expansion of legal responsibility to the organizaiton itself regardless of whether they were paid or not.
Its not hard to see how by using this legal tactic many organizations (primarily on the Left, BTW) could be sued for the actions taken on thier behalf. Could PETA and Animal Liberation Front be sued when animal rights activists slash the tires of hunters or destroy labs? What if some left-wing protestor at one of these anti-WTO events whose bus ticket was paid for by a union cracks someone in the head with the sign? Will we then see lawsuits against the union that paid for the bus ticket?
I have a feeling though that this standard will only be applied to the Politically Incorrect.