I wonder if anybody has figured out that Beiber was in the right there and the questions he was being asked were completely inappropriate and had nothing to do with the case...
Actually, I wondered that - but then I realised that they are probably trying to judge whether those people might have information about the incident. If he was dating Selina at the time, then it might make sense for them to call her as a witness. Ditto, if he usually turned to Usher for advice on dealing with stuff, then they might call Usher.
Apparently, a deposition is an important stage of the process - if Bieber's team wanted to state that Selina couldn't possibly know anything about it and shouldn't be called as a witness, then they'd probably need to start making that clear at the deposition stage once the opposition team started down that route.
It sounds like a strange question, because it's probably designed to put him off balance (lawyer style approach) before they then ask what they really aim to ask. "So, was she around the night of the alleged incident?" "Did you talk to her about the incident?" etc.