Hi there. It’s not really a mistranslation - the word 文明 (bunmei), “civilization,” is actually there in the original Japanese. But it doesn’t mean these phantoms literally built cities or societies (they're not ghosts). In this context it’s more metaphorical - they’re saying: *whatever this thing is, it tried to become something structured, advanced, ‘civilized’ - but it failed, and what’s left is a distorted wreck.
So “a failed civilization beyond human understanding” isn’t literal history, it’s more of a cosmic-horror way of saying it’s an aborted or misbegotten form of life, something that never should have existed.