Culpable homicide was the view of the first trial judge, who seemed quite sympathetic to him, not sure why. But she also argued that the prosecution had not shown or proved that he intended to kill Reeva, which I thought was a good point. Although I don't know how you can show that, unless he shouted, I'm going to kill you. Apart from that, it's inference.
However, the argument that it's murder in any case, is quite strong. You can't just shoot burglars - the US has a terrible record of parents shooting their kids, creeping home drunk. So they pay a heavy price for their castle doctrine. Having said that, don't really know SA law.