Isn't that a bit like saying, for every soldier that has lost a limb while in service, and survives, is going to pass on a mutated gene that produces humans that are born without arms?
Which suggests that these mutations are based upon psychological distress, and that the animals are choosing their genetic evolution...
That's fascinating, and leaves a lot of scope for a future evolution of humans, simply by applying the mind!
Well I guess that's what they meant when they said "mind over matter"
Although there are some interesting hereditary environmental epigenetic changes, evolution (as we understand it) is driven by selective pressure.
Your soldier analogy is great because it perfectly describes what evolution doesn't do. We know that an armless veteran is not more likely to have an armless child.
As for the elephants, the way poaching causes evolution is by killing (not maiming) only elephants with tusks.
So in the past, it was an advantage to have tusks. An elephant with tusks was more likely to survive and reproduce.
But with poachers killing elephants with tusks, it has reduced the likelihood so much that it may be better to be an elephant without tusks.
Because tusks/tusklessness seems to be heritable, this combination of circumstances leads to an increase of the ratio of tuskless to tusked elephants.
The animals made no choice. That gene appeared randomly from mutations, no elephant made a choice to introduce it. Then evolutionary pressure, and more specifically in this case the fact that poaching is the biggest danger those elephants face, has made that gene spread across the population of elephants compared.