My 2 cents worth. I don't believe in the term AD, unless it's referring to a weapon that fired without benefit of any human intervention. I prefer to use ND (Negligent Discharge), when a human is involved...more descriptive.
One of the responsibilities of firearms ownership is Safety (with a capital "S"). When an ND occurs in a match, even a matter of inches off, it's still an ND. Most of us have done it; that's why we have several rules for safe handling of firearms. Even if one is broken, the others should serve as redundant backup to keep us safe.
The disqualification is not extreme IMHO, given that it's only a competition. The lessons learned by that shooter, in his disappointment, may keep him out of a *real* ugly court battle some day, should he have occasion to use a firearms in defense of life.
I don't want to make too much of it; but I hope he didn't either.