There is no right to refusal at border control. It's outside the 4th amendment so it's not even relevant.
Also note that Miranda rights are not constitutional rights.
This guy requested not to proceed without his lawyer present several times, with no result.
It seems to be more true than it did a couple of decades ago, what with more recent rulings like US v. Cotterman and US. v. Koluz better clarifying what counts as a routine border searches vs. more in-depth "forensic" searches that require individual suspicion.
you'll find it's the same people