The USA calls it B-1.
https://www.uscis.gov/working-in-the-united-states/temporary...
(I have no comment on the relevance of this to the article.)
What?
You simply say you're traveling on business, you absolutely do not lie and say you're a tourist.
This case is additionally complicated as some of the construction work was being done by Latino workers who (like many construction workers) may not have had valid immigration paperwork.
In particular, worker training and equipment installation/setup. This seems to be exactly the case there.
https://travel.state.gov/content/dam/visas/BusinessVisa%20Pu...
I don't think this greatly changes your general point. It's likely that many of those detained were in fact lawfully present.
But what about assembling and installing the battery presses? Or maybe setting up the electrical connections for them?
It is a genuinely ambiguous area, and I won't be surprised if Korean companies tried to push it a bit too far. This still doesn't excuse the ICE behavior a bit. They could have just revoked the visas and asked employees to leave.
It's also quite clear that the Korean companies were not flying engineers here to save on wages.