Item RB353723233CN was received by China post on 16th December and no other tracking information has been updated. Is this due to it being Christmas time? Also the seller has told me that it has arrived in the UK, and sent me this message;

RB353723233CN 查看官方数据 中国 查有信息 英国(修改) 查无信息 2013-12-16 00:00, 收寄局收寄, 南京市邮政局函件广告局, 英国 运输途中 概要 复制 目的国家 - 英国:查询耗时:1497 毫秒 发件国家 - 中国:查询耗时:0 毫秒, 缓存时间:2013/12/21 17:45:48 2013-12-16 00:00, 收寄局收寄, 南京市邮政局函件广告局, 英国 Project has arrived in the UK.You can receive at once.Please wait.thank you

Could you please tell me what they mean and how they would know if the tracking information hasn't been updated?

I know that, but the question was, what do they mean by that it has arrived in the UK because how would the seller be able to know if the tracking information hasn't been updated?