No, they merely have to reasonably believe such a threat is imminent...
This isn't really correct.
If my shorthand summary wasn't clear, I apologize. For clarity, let me describe the underlying principles in more detail to explain why the statement you made and that I've quoted here isn't quite correct.
All elements of the Ability-Opportunity-Jeopardy (Manifest Intent) triad have to be present simultaneously to justify the use of deadly force by a defender against an attacker. Note that the following definitions are carefully written. Every word matters.
Ability: does the attacker have the power to kill or cripple, either through possession of a deadly weapon, through disparate force (numbers, physical size, etc.), or because the defender is in a position of physical disadvantage and unable to fight back?
Opportunity: If the attacker has a contact weapon, is he close enough or otherwise able to actually use the contact weapon to injure or kill the defender? If an attacker has a distance weapon like a firearm he can fulfill Opportunity at a very long distance.
Jeopardy (Manifest Intent): Has the attacker, as shown by his words and/or actions, manifest the intention to cause great bodily injury or death to the defender, as construed by a reasonable and prudent person?
Merely believing/suspecting/supposing/being worried that an attacker might have a deadly weapon does not satisfy
Ability. The defender must know ("see"), or at least be able to truthfully claim that he thought he saw, that the attacker had a deadly weapon, in order to satisfy this element.
In this case, the store owner told the local TV reporter, with the camera rolling, that he did not see a gun or other deadly weapon, and this statement was broadcast worldwide. With that simple statement, he effectively eliminated any future claim that his attorney might make that he perceived that hoodie dude might have possessed a deadly weapon. He basically admitted that
Ability was absent. Not too smart.
But the mere open possession of a deadly weapon only satisfies
Ability. The other two elements must also be met. Simultaneously.
So, let's apply AOJ to hoodie dude's actions. He didn't flash any deadly weapons (at least not in the video), the store owner says that he didn't see a deadly weapon, hoodie dude was similar in size and age to store owner, and hoodie's buddy was heading out the door (
no Ability). Because he did not clearly show a deadly weapon, hoodie's only contact weapon was his empty hands and he showed no distance weapon (
no Opportunity). It is questionable whether jumping over the counter reasonably manifested any intent to do great bodily harm to the shop owner, but without satisfying Ability or Opportunity, Jeopardy doesn't matter. AOJ is not satisfied.
And, as a result, the store owner does not appear to have been legally justified in using deadly force against hoodie.
By contrast, and just for fun, let's apply AOJ to the shop owner's actions. He visibly grabbed a knife from near the register (
from that moment on, he satisfied Ability). He rapidly approached hoodie (
satisfying Opportunity). And then, with each stabbing motion, a reasonable person could quickly conclude that he demonstrated clear intent to severely injure, maim, or even kill hoodie (
satisfying Jeopardy).
Not understanding the AOJ triad can lead to some disastrous consequences, especially for defenders. And I think that this is probably one of those situations.