Having a solid firearms skillset and training is all well and good.
However, having a solid understanding of the local laws regarding the use of force (including deadly force, displaying a deadly weapon, etc), and being able to make good decisions (especially under stress), is even more critical. You can't call a bullet back, right?
There's also a subtle, but important distinction between just knowing when deadly force may be lawful/justified, and when it's also appropriate for the circumstances.
Dunno anything more than what the article states, but this just occurred in the South Bay Area of northern CA.