In keeping with Hanlon's Razor ("Never attribute to malice that which is adequately explained by stupidity") it's much more likely to explained by poor maintenance and inadequate design.
Hanlon's razor indeed, especially since we're talking about a South American country. I'm currently living here and I have direct experience with how things are done here. Cutting corners is the rule.
The main discussion is at https://news.ycombinator.com/item?id=20195164. Since the current submission doesn't appear to contain significant new information, just that they're investigating, we'll leave the other thread up.
It wouldn't surprise me, but just like other power stations, why the hell are they connected to the internet in any way???
It's such a huge security risk.
I think it would be impossible to completely isolate them. Even if you completely air-gap all the computers in the plant, still the workers carry internet-connected phones. Even if you ban those, the staff can still become target of disinformation when out of work. Maybe the best approach is to just keep it connected, acknowledging the fact that they are potential targets, and then applying sufficient security on all information channels, technological or human.
So that they can bid on whether they're going to be providing power, among other things. Or at least that's the reason I remember for the US.