Was I insensitive/was it none of my business to say this to my son?

Unfortunately Nina we can only guide them to a certain point in their lives and then they have to make their own decisions. He more than likely was angry at himself because he probably felt as though he let you and your heritage down because he chose a different path. I was never raised with a religion either and I needed to find one when I grew up to help me understand myself a little better. You need to explain to him, only if you feel this way, that he choice isn't what disappointed you....that you are just worried that he will forget his heritage. Because that is really what it boils down to isn't it? Maybe if explained that way he will understand better. Although I wasn't raised into my heritage I do still practice some of my native american fore fathers beliefs, at least the ones I learned about on my own. I may not be doing them as correct as I should be but my heart is in it and I know they know this......and that is MY comfort.