I think you are referring to this find from two years ago? The suggestion was that trousers were developed to allow for horseback riding in Central Asia. However, it's hard to say just how old trousers may be because trousers are an organic material and do not necessarily preserve well. What we are left with are the few scraps that do preserve, the interpretation of artwork, and written accounts of contact with previously uncontacted people.

In the case of the later two, Patricia Anawalt (1992) argues that ceramic figures from West Mexico and Ecuador depict breeches as early as 1500 BC with the Chorrera phase peoples in Ecuador and 400 BC with the shaft tomb culture peoples in Nayarit. Anawalt also draws upon colonial accounts by the Spanish with their interaction with the Tarascans, a Postclassic to Contact period people situated around the present-day Mexican state of Michoacan. In all three areas men typically wear breeches with a shirt that is sometimes sleeveless. Anawalt's analysis on artistic depiction of clothing is meant to hypothesize contact between West Mexico and Ecuador, but as I explained the other day harder evidence is needed. Nonetheless, we can say that without older evidence of trousers appearing in the archaeological record before people migrated into the New World, there are at least two independent inventions of trousers in the world. Perhaps the hypothesis that they were developed because of horseback riding is not entirely accurate since the Americas lacked horses until the reintroduction of horses by Europeans.

• Anawalt, Patricia Rieff. "Ancient cultural contacts between Ecuador, West Mexico, and the American Southwest: clothing similarities." Latin American Antiquity (1992): 114-129.