Arguably this could have happened between two brown belts or two green belts, or really anyone.
There are dangerous places to hit someone in the neck (the first thing I thought of when I read this was one such place we'd talked about in class). When the target is the head, whether kicking or punching, Tae Kwon Do, or Boxing or anything else, then accidents can happen , and sometimes do.
It's terrible what happened, but I think it's a reminder that what we do is very dangerous, and though we try to make it as safe and as fun as possible to train and compete, it's *still* dangerous
But I didn't read anything in the article that this was a failure of the tournament rules or the governing organization. The gap in belts between the competitors as detail of the story, but I don't think was the cause.