On the column, there's a panel showing the Sarmatians fleeing from the Romans. Both they and their horses are decked out in scale mail from head to toe. However, no one thinks this is an accurate representation of what the Sarmatians would be wearing. Because let's face it....it just seems ridiculous. Can you imagine a rider sitting on scale mail pants while his horse is trotting? Or a horse trying to run with a tube of scale mail around its legs scraping against the scale on its side? This depiction could be based on the scared and exaggerated memory of a survivor, an artistic flight of fancy, or a miscommunication between the two. Elsewhere on the column, hauberks are depicted as spoils of war with no evidence of pants.
Ammianus and Pausanias, two classical authors from different centuries, both describe Sarmatians as wearing scale cuirasses made from horse hooves. Pausianus mentions that they are sewn on with horse or cattle hair and Ammianus adds that they are sewn to a linen shirt. Neither of them mention scale pants. Frustratingly, though, no hoof cuirasses have been found in any Sarmatian archeological finds. I haven't done much serious research into Sarmatian armor, but current opinions seem to hold that a mix of metal scales and lamellar plates are more likely/common.
Ammianus Marcellinus, Res Getae
Brzezinski, R., and Mielczarek, M., 2002, Men-at-Arms: The Sarmatians 600BC-450AD, Osprey publishing.