I don't think the article states that the improvement in performance isn't the same for intel CPUs.
maybe they just optimized the game.
Benchmarks with Intel vs AMD here:
https://www.pcper.com/reviews/Processors/Ashes-Singularity-G...
Whatever they did for AoS significantly increased 1800x performance while keeping 6900k performance essentially flat.
No, Intel gains 0% vs AMD gains 17-20%: https://www.pcper.com/reviews/Processors/Ashes-Singularity-G...
The big news is that on the Ryzen launch day, despite benchmarks in general looking outstanding, the gaming ones were somewhat disappointing. AMD said it is due to software problems (eg. detecting the CPU vendor through cpuid and enabling Intel-only optimizations only for Intel CPUs). People seemed to be dubious or overlooked this.
But now AMD proved that with software-only optimizations that took 1-2 weeks they were able to boost the Ryzen gaming performance by 15-30% on the 2 major games they worked on.