Upvote:2
Such a person would not get to photograph my (sole) passport in that manner.
I'd want to know who they were, and would probably ask them to take me to an official point of contact OR suggest that they come with me to the airline's help desk.
While it may well be legitimate I have never experienced anything like this in dozens of flight to, from and in China so would want to know that I was not facilitating identity theft or some other such unofficial behaviour.
That said, not annoying people who do have a right to do something and who may have right of 'fly or stay" over you, is always a good idea and no less so in China.