I am not making a political posting because this can and has happened for quite some time under different administrations.
There are TV shows which come under various titles such as “To Catch A Smuggler” wherein people crossing the border are asked why they are coming to America, for how long and so on. Some may be visiting, some coming to work, some carrying drugs or lots of money and so on.
The Agency is looking to ensure that people are not sneaking across the border and have a reason to be here. There have been people shown who have the wrong visa (like to attend classes) whom the officers believe are here to work and perhaps overstay their visa. There are a few stories where it appears the cild with the adult is not theirs. Also many stories about drug mules with drugs in their luggage, on their person or inside their body, etc.
One flag Officers look at is to whether people have specific plans and funds which match the time they will be here and whether those plans include hotels and specific things and places they intend to visit. Someone arriving with little luggage, no hotel, no plans except vauge plans to sightsee but have no places they can mention they want to see, have no return ticket and not enough money to be here a week. That raises flags.
I have not read the article, however I am betting that the some of the above raised the issue. These detainments are more obvious after 9-11 and now under increased pressures from the Government.
I encourage you to watch some of the TV series, usually avialbale on streaming services and perhaps Youtube, to see what happens and how illegals and drugs are found. Yes, they also show patrolling the border and capturing illegals entering the country from the south.
Here is an example of the types of things they encounter at the borders. https://www.youtube.com/watch?v=BI9IsTPbko0