Guns don't accidentally discharge.
People accidentally discharge them, as was the case here.
Guns don't accidentally discharge.
Guns in proper repair don't accidentally discharge. I have seen guns that would fire on their own, due to work or broken sears, etc.
But I agree with your point. If a gun goes off because someone pulled the trigger, it wasn't an accident. (And if a gun with a worn sear goes off because someone who knew the sear was worn put ammunition into it, it wasn't an accident.)
Accidental discharges are possible, but they're extremely rare. Most so-called accidental discharges are better described as negligent discharges. And this incident is most definitely one that should be referred to by the latter term.
Guns do accidently discharge if you drop them, etc. However, when you pull the trigger it is not an accidental discharge.