BIB - I think what it proved is that when he took the exam, and perhaps by extension, when thinking rationally and reasonably about it, Pistorius knew that shooting at an intruder was only acceptable if his life was in genuine danger. But in pistorius's case he says he did believe it was in danger, (even if we know in hindsight that it wasn't.) And if you lived in SA and heard an intruder in your house, metres away, at three in the morning, you may well believe you were in danger.
I also think, that had he thought reasonably and rationally about it at the time, he would have realised that an attack on his life had not actually begun. However, I don't think he was thinking rationally and reasonably, (Just like Boshoff,and just like Mdunge)- instead, the panic and fear from the belief of an intruder, would have impacted on his ability to think calmly and clearly.
If he believed there was an intruder, it is understandable that he believed his life to be in danger.
If he then heard a noise, believed the door was opening and that an attack was beginning, that would have confirmed his belief that his life was in danger and so in responding by firing, he might (wrongly) have believed he was still defending himself within the law.