I feel like "subcontractor" here could mean "staffing agency used by Hyundai to shed liability", but could also mean "equipment vendor". The latter seems much less likely to be noncompliant, since they get the special benefit of the policy we're discussing and since customer-site labor is a smaller share of their cost (since their primary business is building the machines in Korea).
A lawyer for some equipment vendor staff seems to be alleging that their B-1 applications had been drafted specifically to comply with this policy:
> Kuck said letters included with visa applications that he reviewed spelled out the scope of the work and appeared to meet requirements.
> "It was more detailed than some of the letters that I've written for clients in similar situations," he said. "The vast majority of folks, including the ones I represent, should never have been detained."
https://www.reuters.com/business/retail-consumer/lawyer-says...
I guess it's likely that at least one person detained was unlawfully present, and at least one person detained was lawfully present. The actual ratio is still unknown, but the reputational damage is done--"we took you away in chains, imprisoned you for a week, and deported you, but that's okay because a different worker at your site was noncompliant" is not a great message.