The history to this is through the Apache "survival" and "fighting". The knife, tomahawk, bow and arrow, and then later guns were utilized as they served the needs of the people. The knife was a primary and savagely utilized weapon of Native American's in general, the Apache tribe as well (scalping, skinning animals, close combat, main tool in many tasks). These skills are indeed passed down through generations and as similar to other tribes "verbal stories" is the primary method vs. writing them down.
Thus yes this was passed down through the ages of Apache warriors, however, as with any culture many warriors vary and some are not warriors at all. Apache has some militant history which increases the number of warriors and thus would provide a more rich lineage on fighting techniques and styles to a more domestic focused tribe. Strong beliefs and a fervor to survive and prove oneself often are the best ingredients to creating a solid fighting system as well as passing it on to others.
That being said though, Robert Redfeather is the main one who took general tribal training and developed a "system with a label on it". It is also recognized by the masters/grand masters as valid and thus you can say it was passed down through the generations and also developed by Robert Redfeather. Before he, for lack of a better term, "patented" it you could call it fighting techniques that were passed down from generation to generation in the Apache tribes. At this juncture you can also see that Robert Redfeather defined it specifically and thus it's hard to say if there were past "grand masters" of the art or if in the past it was merely practical and depended on individual skills with the need to utilize it in combat.
Frankly though most all martial arts comes from the same general areas in each distinct culture:
- Need of ability in self defense and offense in combat
- Harnessing discipline of the body, mind, spirit
- Maintaining fitness, prowess, and skill to ensure effective readiness when the need arises
You can read about the Apache culture and warfare in general on Wikipedia: https://en.wikipedia.org/wiki/Apache
As you can read the Apache tribe as with many Native American tribes is rooted in spiritual beliefs and it would be out of those beliefs and culture that the knife fighting system of Robert Redfeather is born. I would suspect there would be mixed opinions among Native Americans if the system really represented the true heart of the teachings or if it was turned into more a commercialized style.
P.S. Also note that Robert Redfeather also is into martial arts in general and I doubt the style is 100% just Apache instead of adopting useful body mechanics and custom styling from his experiences to enhance the core Apache teachings.