Your grandfather was probably brought up in a boarding school,which the elders wont ever really talk about it for what they were put through.
I mean just imagine they take you from your home,take your name ,your heritage,beat you repeatedly for using your own language.
You get sick and die you are buried out back with the other sick kids and your parents wont ever hear from you again.
Just given an opinion based on what you said about your grandfather and the possibility of him being native american.