It can be lots of things, but the context of something like Sigil or spelljammer is
critical in this case because those are setting bridging things that claim to be the most advanced by cranking up the cargocult & simply saying that x has high status in the "shared" multiverse that applies to every setting, that Y god is above all others, Z plane connects to every setting, etc while not pulling from any setting that is or was more advanced than FR & Greyhawk.
When you have
this nonsense
then Sigil
damned well better be at least as advanced as blue/green age athas or some of the advanced civilizations in eberron
(khorvaire is very advanced but not the most advanced ever & some of the others that still exist are more advanced in some ways). You can't embrace that level of superiority without actually
being superior.