As antlersoft implied in his answer, the Salt Vampire was obviously inspired by Coeurl in A.E. Van Vogt's "Black Destroyer" (1939).
And the odd thing about Coeurl is that there are two somewhat different versions of Coeurl.
A.E. Van Vogt wrote several stories about the harrowing adventures of the crew of the Space Beagle and eventually he rewrote all of them as part of a "fix up" novel, The Voyage of the Space Beagle (1950) with a new character as the protagonist.
Coeurl is different in the two versions. In one he has suction cups on the ends of his large tentacles, in the other his large tentacles divide into smaller, finger-like tentacles. In "Black Destroyer" Coeurl needs the chemical compound phosporus to survive, in The Voyage of the Space Beagle Coeurl needs the chemical element potassium to Survive.
As far as I remember from a recent rereading of "Black Destroyer" Coeurl was a member of the civilzed species which left the ruins on the planet. But as far as I remember from reading The Voyage of the Space Beagle long ago, there was speculation that the Coeurls might have been an artificial species created by the biological science of the natives of the planet, perhaps created as some sort of biological weapon. Coeurl was an intelligent being with some knowledge of technology in both versions.
So I have to wonder whether George Clayton Johnson, writer of "The Man Trap", and the production staff, were more inspired by "Black Destroyer" or by The Voyage of the Space Beagle, and whther they considered the Salt Vampire to be the same species as the natives who left the ruins or a member of another species, a species which might have exterminated the natives.
In the second case the Salt Vampire would not have to be as intelligent as the builders of the ruins, though it might be. I note that the Salt Vampire wears clothing of a sort in its true form.
I have woundered whether Salt Vampires were created as a biological weapon to seed on a planet and kill off the native intelligent life, and then die off from lack of salt before their creators colonized the planet. If Salt Vampires were seeded on several planets that might explain why Trelane had a Salt Vampire statue or mummy in his place. I have also wondered whether Klingons might have been created as cannon fodder by another species who they later turned upon.
There is a thread at the Trek BBS discussing why didn't they just give the Salt Vampire table salt: