If you read the article you would know this is all being done via cloud gaming. So the phone isn't doing the processing/rendering. Its just being given a stream that you can interact with. Latency and honestly I imagine graphical quality will suffer due to compression but maybe AV1 encoding will give it a bit of a lead. I'm not saying this isn't awesome but its no secret cloud gaming may not have great longevity and I doubt Apple is going to let you keep your copy of _________ if they ever shut down the service.
This is apparently incorrect, these are running natively which is surprising. So I will retract my former statement but keep it for posterity .