I assume that a person's background contributes to their ideas in some way (cf. Whorf/Sapir), hopefully not to their credibility. I'll let someone else come up something here.

I am most interested in the fact that he said that his theory could not be improved by drawing on thinkers from other cultures. Why? Because his theory itself implies that other cultures have things to contribute.

As he said, cultures have more intelligence (i.e. better theory creation powers) than individuals. One would guess, then, that he would say a good theory should maximize the number of cultures it draws from and the degree to which it draws from them.

However his theory is at best the product of one culture or at worst (and I think this is what he implied in his question and answer response) the product of one individual.