That's how evolution works, isn't it?

Usually, there is just a higher rate of non-reproduction in the less fit individuals, rather than wholesale death, but yeah, that is how evolution works.

evolution is so discriminatory

No, that is how Natural Selection works, not Evolution. This is a demonstration of natural selection, as the resistance was already resident in the DNA. Natural Selection != Evolution.

Natural selection is a crucial component of evolution.

> This is a demonstration of natural selection, as the resistance was already resident in the DNA.

It doesn't matter which came first, the external pressure or the genetic trait. In both cases it's evolution.

Natural selection is a major component of evolution. The other is mutation, which produces the variation that natural selection operates on.

The paper specifically based its analysis on SNPs, a large fraction of which are novel mutations that did not exist in preexisting fixed alleles.

To select you need to have options to select from.

This is exactly how evolution works though. The genetic makeup of an individual organism doesn't change according to its environment. Only the offspring can have different genetic makeup which can be for better or for worse - this is where natural selection comes into play.