"The Sculpted" is the word used to refer to any non-human inhabitants of the world of The Spire. All of them are different from humans in physical appearance, often quite drastically.
"Skew" is a derogatory term used for Sculpted
Sculpted were made by humans, but they most likely (at least according to the author 1 ) descend from humans. They also take on more dangerous jobs (that's what they were made for).
The city is also surrounded by "vapor", where humans can't (and don't) live without masks. Sculpted live there just fine.
Even Sculpted occupying high positions are sometimes disregarded
Skulpted occupy lower tiers of the Spire (tier ~= social class 1 ), but apparently work hard:
A group called "Zoarim" are religious zealots who see the Sclupted as abominations and kill them (and use their body parts to make stuff)
There are nomadic religious groups who live out in the wilderness beyond its walls who are far more hardline in their zero-tolerance approach to non-humans — as they’d call them — than anyone inside the city. 1
People are not happy because apparently Sculpted come to the Spire (the city) and "take their jobs" (because they're better suited, really)
The author claims 1 that the xenophobia in The Spire is inspired by the modern world:
But, as we know, living in the armpit of hypocrisy which the Western world often becomes, it’s one thing for a society to claim to be egalitarian and color-blind and free from all prejudice; it’s quite another for its people to actually live, think and act like that. And that’s what’s going on in the Spire.
Spurrier didn't link Sculpted to only one social group. Which social group is he trying to represent here?