The "iron bird" portion can't be a reference to a year. That's ignoring the male and female system of the Tibetan lunar calendar, if the iron bird was a reference to a year it would have a male or female tag on it. Also, why do they mention the horse? The horse is also an animal in the Tibetan lunar calendar. Is that a reference to a horse year too, since it's right next to the iron bird portion? It makes far more sense in reference of modern transportation.
Everyone sees it as a clear metaphor for planes and cars from the 8th century. Not just the Kagyupa.
His Holiness the Dalai Lama visited the Navajo Nation one time, that's also a good example of the Dharma coming to the land of the Red Man (basically the Native Americans' homeland).