I think the court is saying is that if you are a resident of Pennsylvania who happened to have (illegally) graduated from a California High School, only then would you be eligible for in-state tuition. That’s the pretense of consistency that this court decision offers. Of course there’s no logical reason why someone from Pennsylvania would illegally attend high school in California, but there is a huge incentive for someone who entered this country illegally to get a free high school education in California. And that incentive has just increased substantially with the offer of subsidized college education costs.
Actually, you raise a good question, facetious or not. I have not yet seen the entire opinion published online. But, it will be interesting to see if the opinion carves out any residency requirements for the illegals. If it doesn't, I'm not sure how they could deny your posited scenario.