Hi Joel. I am glad to hear you are recovering. I guess you got broken in the hard way. I have been fortunate in my bike riding years to have never been in a scuffle. But I have taken many tumbles off of horses, primarily racehorses moving at high speed. While my jockeying days have finished, I can tell you that the most common injury with horses is...the collarbone. Most jockeys are very good tumblers, but the truth is, the way we fall, landing on our shoulder, eventually you are going to be with enough pressure in the wrong position, with a bending and it breaks.
I don't know how you fell, but unless you hit something solid, like a rock or curb, my bet is the jacket would not have saved your collarbone. Don't get me wrong..I ride with an armoured jacket all the time; I like my body parts to not get scraped off or punctured. Same with pants in cold weather. Its a must have in my view. Just don't blame yourself for not having one in this case.
Not sure why you are responsible in an accident caused by someone else...
Ge well soon.