Rhinos have been killed by humans by the hundreds of thousands over the last 30 years.
There's nothing natural about that.
Anything that's incidental to changes in the animal's environment, including increased predation or habitat destruction, would still count as natural selection. That includes cases where the predator is a particularly vicious species of great ape.
What does natural mean then? It's not like they disappeared by some magical event or an asteroid falling on the face of the Earth.
In the case of poaching, poachers are not intentionally trying to change the phenotype of the animal. They want to collect the horns/head/etc. The selection itself is an emergent side effect and, I would say, the natural result of a highly effective predator being introduced into the environment.
It is worth noting that the word natural is itself not "natural", the word is a human invention used to separate our own activities from others.
Nope, that's not natural in my book.
I am a bachelor in Biology besides the computer degree and this is something I perceive as a deep loss not because of this specific specimen but because of the trend it again confirms. We have modified the key features a species need to survive because of the way we are and big beautiful beasts like this are essentially doomed unless we change our ways, which I am very pessimist about.
I guess this is something we will need to get used to, it is going to happen more times in the future, our grand children might be the first ones to not see a live elephant or giraffe animals so common in cartoons and they toys will be like dinosaurs for them. It's terrible to think about it.