No, actually.
This wasn't a border crossing; it was an interior "immigration checkpoint".
At interior "immigration checkpoints" (which are complete bovine excrement in the first place), border patrol agents have authority to detain briefly for one reason, and one reason only: to ask immigration status. In order to detain beyond asking "are you a US citizen?" the border patrol agent must have specific, reasonable, articulable suspicion that the person being detained does not have lawful immigration status.
Thus, without RAS that the driver/passenger did not have lawful immigration status, the continued detainment and order to pull over to the secondary inspection area were both unlawful. As such, refusal to comply did not represent impedance of lawful border patrol agent activities.
From the syllabus in Martinez-Fuerte:
1. The Border Patrol's routine stopping of a vehicle at a permanent checkpoint located on a major highway away from the Mexican border for brief questioning of the vehicle's occupants is consistent with the Fourth Amendment, and the stops and questioning may be made at reasonably located checkpoints in the absence of any individualized suspicion that the particular vehicle contains illegal aliens. Pp. 428 U. S. 556-564
https://supreme.justia.com/cases/federal/us/428/543/
1) Border Patrol
2) operating checkpoint NOT at the border
3) can stop and ask WITHOUT RS and
4) it is consistent with the 4th Amendment
So, they might have thought the driver was an illegal, or they might have had a hunch that he was transporting illegals. It doesn't really matter.
You may not like it, but that is what the SCOTUS gave the BP. The agent citing the case to the driver was correct. Under the case law the BP could direct him to a secondary area for questioning, w/o RS or PC.
If they then want to conduct a search, then they need PC or a warrant.
The case seems pretty clear to me, and it was a 7-2 decision.