A third possibility is that blame is assigned to the operators for political reasons.
On a related note, people seemed to be really focused on blame. The question of who (government, corporations, individuals) is to blame comes up all the time. Personally I don't see this as a very important question. I mean let's say we study the situation and decide to blame the operators. Then what? What have we gained? A scapegoat? That does nothing to help us make future decisions.
I think the focus on blame is a distraction from our understanding of the situation as a whole. The chain of causation never really ends. Even if you could single out a individual operator as the cause of an accident, who hired them? trained them? Why does one person have so much power without oversight? Why were their actions not noticed? What aspects of the culture of nuclear power allowed this to happen?
Maybe companies always focus on profits over safety; in that case, maybe nuclear reactors should be state-owned or not exist at all. Maybe the governmental oversight failed; maybe anyone should be allowed to inspect the reactor, or the IAEA should be funded to do regular inspections. Maybe one operator did something wrong; maybe hiring practices should be revised, or maybe any important decision should be signed-off by two senior engineers.