Considering the think layer of sarcasm above, it's pretty clear the booing was joke as well. Same thing for sitting with crossed arms on the front row while everyone else cheered at the jackpot demonstration.
I thought it was part of who the author is. He doesn't strike me as a particularly serious person, so booing the security researched who has become a "star" of Black Hat in the eyes of the rest of the applauding audience sounds like a funny and friendly thing to do to me.
