Case law disagrees with your definition of PPD because a genuine fear must be based on rational thought, otherwise any murderer could claim that they had a genuine fear and then be exempted from dolus based on PPD. This was mentioned in the SCA judgment:
"But as was pointed out in DeOliviera ,the defence of putative private defence implies rational but mistaken thought. Even if the accused believed that there was someone else in the toilet,his expressed fear that such a person was a danger to his life was not the product of any rational thought. The person concerned was behind a door and although the accused stated that he had heard a noise which he thought might be caused by the door being opened, it did not open. Thus not only did he not know who was behind the door, he did not know whether that person in fact constituted any threat to him. In these circumstances, although he may have been anxious, it is inconceivable that a rational person could have believed he was entitled to fire at this person with a heavy calibre firearm, without taking even that most elementary precaution of firing a warning shot (which the accused said he elected not to fire as he thought the ricochet might harm him). This constituted prima facie proof that the accused did not entertain an honest and genuine belief that he was acting lawfully, which was in no way disturbed by his vacillating and untruthful evidence in regard to his state of mind when he fired his weapon."
Exactly.
We have covered this ground before in huge detail
The question is not what the accused claimed to have felt (fear etc), but what the accused must have known.
That implied knowledge must then meet the legal standard for PPD
As in other jurisdictions, the SC has consistently held that PPD is a high standard to reach - for obvious reasons.
So - as all 5 judges concurred - where no rational person could have believed that an attack had commenced / firing was justified - then prima facie OP also must have known that
The onus was thus on the defence to prove that he actually did believe it and did believe he was entitled to fire.
Of course no such evidence was forthcoming