

I auto-translated the Korean article on this because it has more detail.
https://n.news.naver.com/article/015/0005180971?sid=101
Sounds like the majority of people picked up were in fact Korean citizens working under false pretenses. They used b1 visas and ESTA (non-visa travel authorization) meant for things like personal travel or international meetings, but not productive work like constructing a new facility.
The fact that they were Korean insinuates that they weren’t doing run-of-the-mill construction tasks because that could be handled by local firms (who would probably be hiring local Latino workers): they were probably there for much more technical work.
Hyundai would have known this, and would have been intentionally breaking this law. This sounds to me a lot more like a big company actually getting consequences than what ice has been doing raiding small businesses and home depot parking lots.
Im definitely not a lawyer, but here is a government link.
https://travel.state.gov/content/travel/en/us-visas/tourism-visit/visitor.html
Permitted activities under b1 include
Not permitted include:
Also on that official site, it says the permitted activities for visa-free (ESTA) are the same as B visas.
The US government actually doesn’t care who is paying for the work, what matters is if the work is taking place within the US, it requires a proper visa (or esta).