Well, alloys smelted by ancient methods were full of impurities. They could be saying "This bronze contains traces of arsenic and lead in a ratio consistent with artifacts from location X and time period Y." But I thought Tezumak was supposed to hale from some unknown, completely forgotten civilization.
Maybe 'radiography' really means neutron activation?
It might. In fact it probably does. Some quick googling tells me that neutron radiography is better at revealing the internal structure of metals than X-rays, and that this is useful to archaeologists because it can show what methods were used to manufacture metallic artifacts. That could indicate when and where something was made, but again, in this case you'd need other examples of Tezumak-era metalwork for comparison.