The Bright Way is not considered to have a single founder. The faith is said to have been revealed to the entire newly sapient yinrih species in an event called the Theophany. It is here, while the yinrih were still hunting with crudely knapped flint paw axes and storing edible seeds in nothing more than holes in the ground, where they received the Great Commandment to seek out other sophonts among the stars. And it is thanks to their monomaniacal pursuit of this Great Commandment that the yinrih went from the paleolithic to orbital flight in a mere 5 millennia.
Pictured above is a depiction of what was seen during the Theophany. It is an orb of light with a fringe of shifting hues, hanging in a part of the sky where the sun did not travel. Despite occurring at midday, the rest of the sky was dark as night and the stars shone unusually bright.
Over time, depictions of this vision evolved into the star and gear used as the Bright Way's usual symbol. The gear evolving from the chromatic fringe around the orb. There is considerable debate inside and outside the Bright Way as to what this glowing orb was. The majority view in Claravian circles is that it was a breach between the realm of the knowable (the physical universe) and the realm of the unknowable (the Empyrean). While not explicitly endorsed by the magisterium, a common assumption is that the light was in fact the Uncreated Light itself, or more accurately, the closest a mortal mind could get to perceiving the Light's inapproachable glory.
If you ask secular historians, especially within Partisan Territory, it was an instance of mass hysteria, possibly having to do with the yinrih's newly sapient brains. But there are multiple accounts of the Theophany that are reasonably congruent with one another that were penned (clawed?) far away from one another, with no time for one group to have been influenced by another.
Others think it was a hallucination brought on by tainted water or a gas seep that collected along the river valley. A disaster of this magnitude would surely have resulted in other negative effects, like dead animals or sick pups, or at least lingering issues with adults that would have been documented. The fact that this is not the case, especially given the strong taboo against intoxication, makes this idea hard to square with what is known.
Perhaps it was something akin to an aurora, but at that time of year? at that time of day? on that part of Yih? localized entirely within a single discreet orb? Highly unlikely. It also doesn't explain the darkened sky.
They are in fact in awe of human music, but it's more because we can put words to a melody and they can't. Yinrih phonetics relies much less on different qualities of sound and more on timing pitch contours and volume envelopes. They can't sing words because the rhythm and melody would obscure the meaning far more than a human singing Mandarin or Vietnamese, for example. Most of their modes of speaking are also very quiet compared to humans. Imagine this but modulating the pitch and volume of the growls.