Reason is trying to make this viral..
We came across one of these on a trip across the southwest last year. It was at least 50 miles from the border, in the middle of nowhere. We had no idea what it was about while pulling up. They asked if we were citizens of the US, we said yes, they said move along. OK. But after driving off the comment was "why did that just happen"?
Basically they are suspecting everyone driving down the interstate of being an illegal alien until you say otherwise. They aren't asking anyone to prove it by showing ID, but chances are if someone looks nervous--or maybe Hispanic--they will try to detain you if they don't like the reply.
Even the Arizona bill didn't allow cops to ask for proof of citizenship without having a valid reason to pull someone over or detain them on the street. The Obama administration sued over it, yet their own CBP agents are out on the interstate asking everybody in every car about their citizenship without any probable cause to suspect they aren't citizens.
And now, the DHS has released actual detained illegal immigrants from lockup--an illegal move--to score political points. Yeah, good thing that ole Bush is not still in power.