I'm guessing it was staged...
I kind of doubt otaku would throw big slumber parties, they most likely prefer private time with their pillows...
You'd be surprised what people and especially otaku would do.
I remember watching an MTV documentary on people with fetishes for big furry animal costumes. They called each other "furries" and it went as far as describing how "furries" have sex with each other. They would cut holes in the genital regions of their big furry goofy costumes and then do freaky crap with each other while in costume. Funny as hell watching Wally the Moose making it with Daffy Duck. The participants weren't always guy/girl either. Anyone else see this documentary? It was something like "True Life - Furries" or something like that. Anyways, this otaku slumber party seems tame in comparison.
Don't believe me? Check this link out (don't worry, it's clean, just a transcript of the MTV doc):
http://pressedfur.coolfreepages.com/press/sex2k/