Hello Mr Jitty! Referring to your example, I would say that, whilst understandable, the killer's reaction was unlawful because, in reality, there was no immediate threat to his life. However, he lacked dolus because he had no intention to kill unlawfully. In other words, he probably satisfies the criteria for PPD.
Depending on the circumstances, he'd be likely to get an acquittal; at worst, it's culpable homicide.
Your example provides an interesting reminder that, even looking at the matter from OP's perspective, his reaction was unreasonable. In contrast, despite the putative element, the reaction of the shooter in your example is understandable.
I entirely agree that the wording of Masipa's judgement leaves a lot to be desired and I fervently hope, (against my better judgement), that the Appellate Court will be thorough, watch the recordings, including the screams evidence, and find the means to revisit her tenuous findings of fact.
As the State is challenging Masipa's handling of the circumstantial evidence, ideally, they need to look at the totality of that evidence, not just the excerpts recommended by the Defence.