There’s two types of homeless people. Temporary or chronically. The percentage of chronically homeless who are drug addicts, severely mentally ill, or both (self medication) is around 60-80 (this can vary largely by area).
That’s not to say that drug addicts and severely mentally ill people don’t need help, but it’s like people want to pretend that they don’t exist because they make addressing the homeless issue way more complicated, because at a certain point you have to talk about involuntarily committing people to mental asylums.
Bone char isn’t super high carbon, so it’s possible that either the calcium phosphate or calcium carbonate is playing a roll.
But honestly, you’re probably not getting very much of it mixed in from primitive smelting or forging methods.