The Prop 8 proponents were legally referred to as the defendant-intervenor because they intervened in the CA Supreme Court case to defend the State’s interests because they feared that the State officials would not adequately defend Prop 8. (They were right.) When Walker ruled that Prop 8 was unconstitutional, the State of CA refused to appeal to the 9th Circuit. So Prop 8 proponents (intervenors) did so. SCOTUS ruled that they lacked standing to appeal. So, yes, Walker’s ruling (District Court) stands.
Also, if we're back to the District Court then the title of this article must be wrong because the District Court ruled agaisnt Prop 8. So since District Court's decision hasn't been overruled, then Prop 8 is (at least currently) not good law, right?