To "give" and to "give a gift" are not always, and in all contexts, two expressions for the same thing. I did not think this required citation, but if it does, I suppose dictionary.com is as good as any other internet source. See various entries under
exchange and
trade.
The notion that a person should "give back" to society implies that he has taken something without offering any consideration. It seems to me that that alone is what Williams is addressing, when he says that these people have "given"--that they received their money by improving the welfare of "society."
But I suppose there is no need for us to quibble over semantics. It appears we agree in principle. Those who earn wealth in a free market have neither engaged in charity, nor have they "exploited" anyone (for lack of a better, equally succinct term). They have benefited themselves and society through mutually beneficial exchange; with, of course, the standard caveat that results are not always in line with expectations.