But the poachers would rather breed for elephants with tusks, that's the whole point of their poaching after all.

I feel like I don't really know enough about the specifics of natural selection or evolution to have a strong opinion on this.

The poaching is definitely not natural, so it feels like this is not natural selection.

On the other hand, no one is deliberately breeding for this in any way, it's purely a side effect of these circumstances, which does feel more natural.

You could just view the poachers as an environmental hazard to tusked elephants, in which case this would be a perfect example of natural selection.