Yes, you are right! A scam is not one of the specified crimes. As I understood it from the article, the phone call started out as a regular bondsman scam, but then escalated into threats of harm to the old guy and/or loved ones held in custody at the remote end (?), which elevates the severity, possibly up to a robbery-in-progress. The caller must have dropped the pretense at some point given that the old guy realized it was a scam yet still had the money ready to go in a package on the table. I'd have to read the actual court case to know what really happened, which is too much work, so I wrote my response under the assumption that the old guy was told a family member would be harmed unless he gave the money to an associate who was on the way.

In such a situation, it would be reasonable to initially detain the courier for investigation. If police officers were hiding in wait at the house, they would have done the same thing. It was unreasonable to continue to believe the courier was an associate once it was clear it was an uber driver following an app. So the old guy was guilty for detaining an innocent person without qualified immunity, and crazy for not listening to an explanation of what an uber driver is. Notwithstanding this, there seemingly were threats of physical harm through the phone, so if the old man did treat it as a robbery, and if the courier had been an associate, and the associate did get detained (by the old guy or by the police), and the associate did attempt to escape, there could be a situation where there was an imminent threat that the associate would return to join his accomplice on the phone and the two of them would inflict the promised harm upon the family member they were holding hostage. That would justify the use force up to possibly deadly force to stop the escape. It depends on what exactly was being said on the phone, though again we don't have the court transcript. Unlikely but possible.

Of course none of this happened, the courier was an innocent bystander, there was no hostage, and the old man was totally unjustified for opening fire under these circumstances. But that what the court trial is for. I do not dispute the outcome and I'm glad this person is now in prison. What I don't like is the headline saying a crazy guy shot a taxi driver over some missing change (that he himself misplaced). And then people argue that all self-defense is unjust because it lets crazy guys like this get away with murder. Which he did not get away with. And he was not crazy in the way the headline described it, but was in an intense situation which he might have been led to believe was life-or-death. And in the process he did violate self-defense rules in three specific ways. So we'd better learn the rules, and consider in advance our personal approach to the use of force, so we can act cool under pressure later. It could happen to you too.