Some of the answers to your questions can actually be found in the summary notes I quoted of Dr. Slotow.
Elephants killing Rhinos is a very abnormal situation. The problem arise the moment man puts a fence around a piece of land and call it a nature reserve, a park, or whatever. Immediately man needs to manage this as nature cannot go its own perfect way due to numerous reasons. Man does not always have all the answers on how to manage such systems and sometimes have to learn through some errors made. The dilemma starts because migratory routes are cut off, animals cannot access traditional sources of water, confinement means numbers needs to be monitored and adjusted, etc. Another factor is that there might already be some animals in such an area, but mostly it needs to be stocked with various additional species. Such was the case with elephants.
Because elephants were hunted to the point where there were none left in this province (KwaZulu-Natal) it was decided to bring in some elephants from the Kruger National Park. Those years it was deemed good reasoning (costs, size of the animals, difficulties in loading and transporting the animals, etc) not to bring adult animals to the Hluhluwe-iMfolozi Park. Therefore they brought in babies and young elephants that were the remnant of culling exercises. So, all the adult elephants, all the parents, were culled and the young animals were transported to their new home. This meant that these young elephants had no proper training and preparation for their adult life. Because there were no adult bulls around to teach the young bulls they didn't know how to behave towards other animals or how to react to the hormones once they became sexually mature.
Unfortunately the Rhino population carried the burden by being attacked by these young problematic animals. I quote Dr. Slotow again: "This behaviour was ascribed to young bull elephants in musth. Musth is a state of heightened aggression associated with reproduction, and the young elephants are entering musth at around 18 years old, instead of at about 30. The normal pattern is for bulls to gradually enter musth, with the period lengthening with each event. The young bulls are entering full musth for up to 3 months at a time!"
Eventually after they brought in a number of old bulls from the Kruger Park and these bulls had time to interact and discipline the younger bulls the problem were solved. Since then I personally have witnessed many moments of close proximity or interaction between elephants and rhinos and all has ended without any negative outcomes.
I hope this shed some light on the matter.
Ubejane Elephant (22) *