they are finding elements that don’t even occur in nature
Neither of your referenced quotes claimed that the elemental makeup of the measured particulate was synthetic. If you are referring to "Niobium and hafnium do not occur as free elements in nature", what this means is that the elements are not ever found on their own — they have only ever been found bonded to something else. Niobium makes up 0.0017% of Earth's crust and Hafnium makes up 0.00033% [source (archive)].