There is a whole bunch of speculation that can be done on this one.
First off, the news agency and the writer may be suspect for embellishment based on their views towards self protection and 2A rights. In my 20+ years of experience dealing with news agency on emergency incidents, they almost never get the facts correct and ALWAYS ALWAYS embellish the story to make it appear more dramatic so it raises ratings and readership. Also many news agencies just copy and paste now rather than investigate themselves anymore.
This story is suspect as written as evidenced by the embellished desrciptors and anti 2A slant it is full of bias and there is no attempt to stick to just the facts.
"thought he was being a good Samaritan" (implying he was not being good)
"he was nearly shot" (implying for doing something stupid)
"(Officers) have a split second to decide whether to shoot or not to shoot," said Callagy. "All he had to do was call police." (implying his actions were wrong and that he was doing the job of police when he shouldnt)
"would be good Samaritan" (implying he isnt)
"charged toward the pair with his gun drawn" (implying reckless behavior of an established -not good Samaritan-)
"The armed man went after her assailant and began yelling. "He was shouting, 'Don't you dare!'" (implying a chase ensued over a long distance, what exactly does "went after mean"? did he chase him several blocks or did he step between attacker and victim and create a defensible space pushing assailant back? description is way to vague)
"The first officer to arrive was a half of a block away when the confrontation began." (implying LE was right there, but they leave out how long it took for LE to arrive if he was half a block away wouldnt he hear or see the altercation?)
"Viola gave up peacefully, but had his gun "in the ready fire position," when confronted by officers, police said. He does not have a permit to carry a concealed weapon, Callagy said" (this one has 2 in it, first gun in ready position superceded and trumps gave up peacefully, and 2nd, concealed weapon was never established, he got out of his car at the beginning of the story, being in a car does not mean he was carry concealed, he could have been carrying LUCC which is legal and requires no permit, but as most CA resident cant get ccw's the truth of him not having a ccw was used against him).
"More than a dozen officers arrived on the scene within minutes, including a police dog, detectives and a traffic officer on a motorcycle. Some carried assault rifles." (minutes? how many minutes 5 or 60? detectives dont patrol usually and k9 units are very few and far between, this line implies that in the blink of an eye a platoon of officers were there negating any reason to be armed in public as a citizen).
"Viola was booked into San Mateo County jail on firearms charges. Police interviewed the man, who was not identified, alleged to have assaulted the 57-year-old woman. The case is being referred to the San Mateo County District Attorneys Office for review".
(booked means taken away in cuffs but notice no mention of the specific charges because they wanted to diffuse the situation take it out of the public eye and straighten the whole thing out downtown. And all of a sudden the 57 yr old was allegedly assaulted by an unidentified man, but in the beginning of the story she was obvioulsy pushed "assaulted".)
If you draw it down to just the facts and they are pretty slim, its 57yr old woman, pushed (assaulted) by a man?, another man gets out of vehicle to assist, a gun is drawn no shots fired, police arrive and arrest. Everything else is fluff and embellishment to paint a picture for people to believe someones idea of "the Story".
It could have easliy been slanted the other way.. "elderly woman assaulted by male gangbanger type rescued by young soldier recently returned from Afghanistan who draws defensive weapon and scares off attacker."
But reality and bare bones truth, an armed citizen DID NOT SHOOT, imagine that, the mere appearance of a firearm stopped the situation from progressing to a negative outcome.
(important side note, tried to post this response to the news site, where all the other supportive 2A statements are, apparently they wont take comments anymore.. huh? wonder why??) Redact this last statement they finally allowed it to be posted by the noon hour.