The stirrup was invented in 300 BC or so in Asia, but still I don’t know of any Asian forces that were famous for their heavy cavalry - the armies of the east were legendary for their light cavalry and hit and run tactics. Still, a horse this heavily armored is made for close-in combat and charging infantry.
It is my opinion that when the horse was domesticated that pants were invented then by the Tocharians, the saddle later by the Assyrians and even later the Sarmatians invented the stirrups. These are all Indo-European people.