1. If a particular passenger fit the description of the subject they were searching for, that would give them reasonable suspicion to detain that person. I reject the notion that they had reasonable suspicion that each and every passenger, male and female, black, white, and other, was the person they were looking for.
2. I don't know what you mean when you say ID can be required in an administrative search when someone is not suspected of committing a crime. Can you provide a cite to that, I'd like to learn more.
CBP's own press release on the matter says that the agents merely "requested" ID, not that they detained all the passengers and required/demanded ID.