Let's remember that the creature never actually craved salt as such. When offered some, it ignored it, instead choosing to kill people for their salt.
Is that proof that it was a dumb animal, incapable of shedding a behavior pattern even when this cost it its life? Or proof that it was a sapient being, capable of ignoring the temptations of the moment in pursuit of a higher goal?
Regardless of that distinction, was it a typical example of its species, or instead a deranged one (a man-eating tiger in the first analogy, a murderous maniac in the second)?
The very biology of the creature suggests that sucking live things for their salt would have been normal for the species. Is this compatible with city-building? Well, perhaps not if the vampires felt the need to suck each other for salt, to lethal effect - but that much was never established. For them, getting sucked might be harmless; or then they had better things to suck than fellow citizens. So there's one niche for the sapient interpretation of them.
Another is a competing species that threatens the city-builders and perhaps ultimately destroys them. Possibly native to the planet, possibly arriving from outer space. But would peaceful coexistence with the putative city-building species be possible, too? The fact that "Nancy" in its desperation still failed to kill Crater for a year or so might support the idea.
We really don't need to know, though. Whatever the true nature of the creature, its most important characteristic was that it gave each and every people exactly what they wanted (plus a painful death, of course). So in-universe, every explanation would be supported by the only surviving piece of evidence, the creature itself! Crater's take on it would be equally valid to Kirk's, and neither could be considered objective.
Timo Saloniemi