The sad truth is Congress is the biggest offender of poor network security practices. Every time they bring in Equifax, DHS, etc to explain why they didn't practice basic IT security due diligence or due care I am reminded of the time smart people were hired to implement basic network security for Congress. Once they realized Joe in IT (who was hired to keep hackers out) can see Congressman Bob has a foot fetish, fish fetish, whatever, Congress told IT to turn everything off.
Just a guess, but maybe the CBP takes pictures of the license plate at land border crossings?
if not pictures, i would say license plate numbers are at least recorded digitally inside of their report.
If they took a decent picture, then they could identify something that looks like the license plate and then use OCR to compute the number and store that.
If only someone could have seen this coming, you know, outside of the thousands of people that saw this coming. This is just one of many reasons why mass surveillance is a terrible.