Wikipedia generally doesn't know what it's talking about ;) Finds of segmentata fittings are relatively common across Roman military sites, mostly because they kept falling/breaking off due to chemical reactions between the bronze fittings and the iron plates, among other things. It's also a matter of debate whether or not these armour pieces were actively used or if they were mostly ceremonial: Goldsworthy, for example, believes that they were actively used, while some others note that we don't have any evidence of the armour's active use. Trajan's column is stylized - a perfect example of that is the shield design, which all re-enactors seem to take as canon (For example, try googling "Roman Shield" - the images will all invariably look like this. An actual Roman shield found near the Euphrates [Iraq/Syria-ish] looked like this.)

For the record, however, quoting directly from Goldsworthy's The Complete Roman Army:

There is absolutely no evidence that auxiliaries ever wore lorica segmentata, used the pilum or, with the possible exception of a handful of units called scutata, carried semi-cylindrical shields.

Hope that answers your question :)