whew...this is tough...you live in Alaska - wilderness - so it's something I would expect people to have on-hand and show their kids how to use it.
however, I don't know your school's policy on things and considering where you live - I don't know if this would be considered an issue.
What bothers me is the kid called it a toy. It's not a toy, it's a tool. Your son should have known it was a tool and not a toy if you have used something similar in your camping with him.
I'm stuck - because the "transaction" took place at the school. However, without knowing their policy and you NOT wanting to get the other boy in trouble - I might look up my student directory and call the parents directly. However, if you don't know them??? See - this is where I'm stuck. I guess I'd just call the parents directly and let them know that their son gave my son their flint wheel and they might need it. I wouldn't get into a "well, this certainly isn't a toy" or anything like that - although tempting - but I would just handle it with the parents. Meet them after school. You don't need to go to their home or they come to yours...unless you live in a small enough community.
I would NOT put my son in the position to handle this. Especially if he's afraid the other boy will think he stole it. **THAT ** bothers me. If the other boy GAVE it to him - why on earth would YOUR son go down "he'll think I stole it" path???