It sounds like they had valid visas (or ESTAs), the question is whether they were allowed to do what they were doing on those visas. That question potentially h

It sounds like they had valid visas (or ESTAs), the question is whether they were allowed to do what they were doing on those visas. That question potentially has 475 different answers too, because there are certain sorts of what one would commonly refer to as "work" that are permitted on an ESTA or B-1 visa, so one would need to know the exact things each individual was doing to make an individual determination. As for why they're pissed off, that seems obvious. If say Australia wanted to have a software engineering office, invited my employer to set up an office, my employer sent me over there to do something related to that telling me it was in accordance with the law, and then the Australia government arrested me, threw me in jail, and posted videos of this all over social media, I would be pissed off too.