WHY did he lie, when the apparent result was an accident?
Because a valid self-defense case results in no charge or a not guilty verdict while an accidental death while doing something extremely reckless results in an involuntary manslaughter charge and likely conviction.
The irony is that self defense requires stating you will fully acted to commit the homicide which if not disproved by the state is Murder 2 while an accidental shooting is Manslaughter, usually.