I have never thought premeditated murder was a starter. I actually have always thought he lost his temper and control after/during an argument. So not so different from your opinion. However, I do think he knowingly shot into the cubicle and directly at RS which is where will have to agree to differ.
I also think if he had been honest with the court he would probably have been given CH as the verdict but with a longer sentence. I have read that although there is not a Crime of Passion verdict per se, that SA judiciary look leniently on offenders who are honest with the court. However, IMO he chose to be dishonest with the court in an attempt to "get away with it" and, for me, that deserves a far greater sentence than he got. I think he shot once, and then chose to fire three more times. That has to be murder IMO.
The following is not the article I read but it came up quickly on a search and to save time I will post this. If you read the article you will see that the woman got away with a minimal sentence for the murder (reduced to CH).
She was fined R2000 (or one year’s imprisonment) and sentenced to a further three years imprisonment , suspended for five years.
http://www.africacrime-mystery.co.za/books/fsac/chp26.htm
Only in France is a crime of passionnel, or crime of passion, a legally recognised defence. In South Africa, a murder committed in a moment of passion is seen as a mitigating circumstance and does not merit special treatment. If the court accepts the view that the crime was committed during a moment of passion, then this usually means that an act of murder is reduced to a lesser charge, such as culpable homicide.