All they know is 16 Psyche has a high density. The earth and 16 Psyche formed eons ago. Some speculate 16 Psyche is the core of a planet that was hit hard in a collision and blew off the rocky stuff - high density might be metal rich. Most common core will be nickel iron with some chrome with a scattering of other metals dissolved if the original planet was a larger. Earth has undergone billions of years of hydrothermal subduction and hydro thermal fluid transport from the deep crust driven by the water/CO2/SO2/Arsenic/silica etc. This hydrothermal fluid is lighter than the basalt, and gradually extracts gold as well as copper zinc etc into the fluid. When it gets near the surface the water/CO2/SO2 leave the fluid as gasses - some stay as carbonates/sulfides/silicates and they form layers - often around volcanos. In deep water they emerge and form nodules - which we can extract metals from. If 16 Psyche's host planet was too small for this = no metal concentration occurred. It waits for some laser bursts to the surface to do spectral analyses to know for sure. Psyche 16 may well be covered very deeply with waste rock gravitationally attracted to it that make surface analysis useless.