Essentially it was already the best mobile chip for gaming, but the extra 64MB of 3D V-Cache has added an extra literal layer of frosting on top of that chip. Or, more explicitly, on top of one of the compute chiplets in that processor.
The 3D V-Cache tech is, more or less, a pretty brute force method of squeezing another level of gaming performance out of your system. There are no fancy algorithms, no elegant changes to the pipeline, just fancy packaging that lumps double the L3 cache on top of one of the twin eight-core chiplets in the package.
Games hugely benefit from low latency access to the vast amount of data needed to render our game worlds. And the closer you can get the memory to your actual processing cores, the faster everything runs. By increasing the amount of L3 cache available to this new Ryzen mobile chip it now has a relatively huge 128MB of memory with which to store game data.