Either one is a Christian or isn't. "Ethnically & culturally" are just b.s. p.c. words to divert attention away from the real thing.
I'm sorry, I was simply trying to convey the fact that Sirhan is a Palestinian arab who is not Muslim, not Jewish, but nominally Christian. I can't think of another way of stating that other than in the manner that I did.
I take it that you take offense at his being described as Christian in some sense. Since I am not certain how to know with ontological certitude whether or not Sirhan believes in the substitutionary atonement, total depravity, unmerited grace, or perhaps nothing at all I don't presume to know quite what he is. Perhaps you can elucidate a more complete analysis of the Sirhan theology for us.