I can see in some rape cases the lines are extremely blurred especially when a lot of drink has been consumed and often it comes down to a "he said/she said" scenario and of course on occasions the accuser has lied. I imagine "negligent in a rape case" is where the woman has rendered herself through the amount of alcohol/drugs consumed vulnerable.
In this particular case, as I understand, the young woman was in bed with the young man having consensual sex, unbeknown to her he had arranged for his friends to burst in on them and then take it turns to rape her, he sat on her chest thus pining her down, whilst some of the 12, possibly not all did that. They then filmed it on their phones. What I'm not sure about, is whether that footage was used as admissible evidence. I think the prosecution tried to build a case that she was complicit in the group orgy and was merely pissed off because it was filmed and that is why she claimed she had been raped. I also read that in the aftermath she was examined and her injuries were consistent with those of a rape victim. It's hard to understand why all the men were allowed to return home, maybe it's hearsay but it has been mooted that some of the parents of the accused rapists have influence in high places.