It's common policy to plan your resource consumption in the most economical way.
Couple that to a "next day" dispatching system.
Couple that to resources that failed to do their job (did not compensate enough reactive power, or even added extra reactive power instead of compensating).
Couple that to one of the most challenging electrical grids in the world.
When taking that context in consideration, "living in the edge" is not really a legitimate way to put it.
That's.. that's a miscalculation alright. But it's not likely that it was just a small math error. It must have been policy to live on the edge.