There's certainly not any primordial knowledge of Einstein's relativity behind the emergence of the ideas of qi. What was the start of it, though, is very hard to know for sure.

My guess is that it began with speculations about the difference between life and death, and the observations that breath was a decisive factor - those breathing were alive, those not were dead.
I allow myself to compare with many similar concepts across the globe, which seem also to have began with speculations about what life is, and what is essential for it.

Quote:
Different theories have been advanced to explain the discovery of the channels. These theories may be summarised as being of two main kinds: 1. points first, channels second and 2. channels first, points second. According to the first theory, centuries of observations of the existence of tender spots on the body during the course of disease, and the alleviation of symptoms when they were stimulated by massage or heat, led to the gradual discover of the acupuncture points. When sufficient points were known, they were linked into groups with common characteristics and effect, and aided by the observation of propagated sensation when they were stimulated, understanding of channel pathways followed. According to the second theory, propagated sensation during the course of massage and more especially the exploration of the internal landscape of the body through mediation and qigong practice, led to the discovery of the channel pathways, with the knowledge of specific points coming later. This second theory received strong confirmation from the significant discovery of a silk book during excavation of the Western Han tomb at Mawangdui, which describes the pathways of eleven channels but does not refer to any specific points.