It has been said that the girl in the video is a model and not a prostitute, and this was filmed in his hotel suite, not the brothel...
Here is a key observation...
He's still got his shirt on. If the boy can't keep his shirt on in public, why would he still have in on if he was just having sex? A more likely scenario is that he and his entourage were partying in the hotel with a bunch of locals and being the wus he is, Bieber passed out in the bedroom, so this girl sneeks in, grabs a few seconds of video and cashes in on her 15 min. of fame...
As for the brothel, me thinks that Beiber took his bodyguards there and payed to watch them give the girls what he really wanted...