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Edit: The elements contained in the alloys must be known. The universe is made up of the same stuff. So what exactly do they mean by "unidentifiable"?

Very good observation. This is a classic example of what the skeptics call 'woo'. Elements are elements. They can be identified through all sorts of methods, even when combined with others in compounds such as minerals or alloys. Claiming that some physical substance 'cannot be identified' is just melodramatic garbage like you would read in (poor) scifi stories.