Or maybe intellectual refers to someone a position in a society that sufficiently is well-off to be able to support some guy not having to provide work for collective survival and who can spend time trying to formalize abstract thinking for which writing would help with (which north americans natives did not have)
It's ok, it can be an interesting culture worthy of being studied, and of course they weren't dummies, without trying to pretend that north american natives were "contemplating concepts like the law of large numbers" without writing device or support nor some kind of alphabet, come on
Yes colonization is awful and yes the natives were genocided but that doesn't mean that everyone was on its way too landing on the moon had they not been suppressed both physically and culturally. The path to civilization only gets narrower and the people who get to contribute meaningfully fewer and fewer.