The ability to selectively express different glue protein genes and/or to extrude their products at different rates provides a faster mechanism to evolve material properties than sequence evolution alone.
The fact that a spider can selectively express different proteins to suit different conditions is no different to all the other ways a living body can selectively alter protein expression to suit different conditions. We would not describe those as evolution.
What do you mean by "we"? Because I happen to have degrees in Genomics and Biology and I would definitely describe that as evolution.
I thought it was saying that spiders were simply adjusting the material properties of their glue in response to environmental conditions. This is not evolution.
The paper is saying that while the glue genes themselves are largely conserved, the material properties can vary by altering the ratios of protein which are expressed.
Presumably this ratio is controlled due to other faster evolving genes (although this is not proven by the paper as far as I can see). I'm not entirely sure if they ruled out whether spiders could in fact adjust their glue in response to changing environmental conditions.
The title is technically correct: the two species share a lot of glue genes, and the properties of their silks differ due to other genes affecting things like the ratios of glue proteins in the silk, and those genes evolved faster than the glue genes themselves.