What you said is true, but what he is saying is about spending your resources. Time, money etc. You may be nice to everyone but due to constraints you may not be able to offer resources to everyone.
That's the point though. If you travel through life only worrying about people that can help you directly, and never stopping to offer help of your own, you miss these opportunities.
The beauty of "charity" in any form is that it sometimes has the very difficult to predict side effect of offering the largest return on investment.
