There is a huge difference between SCOTUS "declines to hear" versus SCOTUS "rules that ..."
Certainly there is no difference to these particular parties. But refusing to hear the case in such an important field as AI is simply an indication SCOTUS is feels it is too early for it to be making rules involving a very fast moving and transformative field as AI.
What it generally means is that the lower court ruling stands and serves as precedent nationwide. Binding precedent in the circuit that handed down the ruling. But another circuit may make a different ruling sometime, and then the Supremes practically have to hear the case to resolve the conflict.
Or that the law is already settled… the ape selfie determined already authors must be human