I think his view throughout is that in the situation where someone thinks they are in danger, as OP was in his mind, the court doesn't take the armchair position and says 'he should have known so did know' but should put themselves in the position of the person to ask 'did he know'? The SCA may have used the right terminology to express this but there is no evidence from the judgement that they made any effort at all to consider the situation he thought he was in and how that might have affected his judgement.
Personally, I think the SA system is foolish to put such an emphasis on such a slight difference to decide between CH and DE given that no judge can really know what the accused was actually thinking - and then it compounds this situation by having minimum sentencing legislation for one crime but not the other.
But this is the same in every murder case and shows you are taking an artificial view
Courts have always asked "what must the accused have known or foreseen"
And that inquiry is based on drawing ordinary and logical conclusions.
It never has been based on trying to delve into the dark recesses of OPs mind
Otherwise no one would ever be convicted