In particular, worker training and equipment installation/setup. This seems to be exactly the case there.

In other guidance, "construction" is specifically excluded from the permission to "install equipment". That's not a very clear distinction, especially for large industrial machines, though I do see their general intent, to permit work requiring equipment-specific skills but exclude work that a locally-hired employee could do about as easily.

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.

	▲	cyberax a day ago \| parent [-]
		But what is "construction"? If it means "building walls", sure. 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.