I imagine an unknown M/V in a border area, furtively operated, would arouse suspicion....mules and jumpers are not unlikely to be operating stolen M/V's, yes? If he had stopped, he might have been all set; but he prolly had a snootfull, and thought they were the local constables, or he had some firearms in the car and didn't want a hassle...understandable: you never know who's behind the badge.
Pictures of illegal immigration invasion on Roger Barnett's ranch, Arizona
http://www.desertinvasion.us/invasion_pictures/invasion_barnett.html
I think it is a pretty safe bet, the BP knew who the guy was. They aren't his biggest fan.
By the limit account given, it seems they knew who he was.
It will be interesting to hear the details.