The suggestion that all these alleged weird alien materials are “alloys” is just a placeholder for “looks and acts metallic, therefore made of metals.”
But if we happened to be dealing with real alien tech, that’s a naive and unscientific assumption. We already have people thinking about how to build programmable matter with variable properties, and it’s a fair bet we’ll have working examples within 50-100 years.
And there is no possibility that conventional x-ray diffraction will reveal how that kind of matter works.