The Beijing institute developed the technique to crack an iPhone’s encrypted device log to identify the numbers and emails of senders who share AirDrop content, the city’s judicial bureau said in an online post. Police have identified multiple suspects via that method, the agency said, without disclosing if anyone was arrested. “It improves the efficiency and accuracy of case-solving and prevents the spread of inappropriate remarks as well as potential bad influences,” the bureau said.
Further read: https://sfj.beijing.gov.cn/sfj/sfdt/ywdt82/flfw93/436331732/index.html
They aren’t saying that the email/number is part of the message. What the are saying is that they are able to decrypt the logs in order to identify the senders .
It could be they cross-reference matching some internal ids / tokens / physical addresses of the devices together with all the data the Chinese government already has (or can obtain) …or it could be a bluff… who knows… there’s not enough information, and what we know is probably distorted.