It's interesting because from what I can make out, closed court means the public and press can't attend so it's a stronger restriction than a non-publication order. If the reason has to do with privacy as opposed to secrecy for operational reasons, I would think the press would argue that non-publication orders are sufficient, closed court unnecessary.
Im sure in the very beginning a female officer said a news brief that his sister was with him..imo i can fully understand why it would be kept quite if that is the case
I wonder whether William's sister is down to give evidence. There was a statement somewhere recently that she was possibly the only witness to the abduction. I don't know whether it was just odd phrasing, but that the sister witnessed or may have witnessed the actual abduction is quite different to what we've heard before.