Not at all - birth in this country is one way of obtaining citizenship, but IT IS NOT THE ONLY WAY. Obviously, naturalization is another way, and there are still others. A more correct statement than Leo's would be "Therefore the term "natural born" must be considered as requiring something more THAN SIMPLE CITIZENSHIP." That clearly is true under the rules of construction.
It may be provable that Obama does not fall under the umbrella of natural born citizen. But THIS particular argument is not proof that "natural born citizen" means a child born to two US citizens. I have seem other arguments that give a basis for that interpretation, but this particular argument is logically flawed. IMHO
I did not see how Donofrio was writing here to define what ‘natural born citizen’ is, but rather that is something more than being born here or as you refine as something more than simple citizenship. Rather at the very end of his piece he refers to Minor v. Happersett where it is unequivocally determined that ‘natural born citizen’ means a child born in jurisdictions of the United States of two citizen parents.
I also failed to see any effect of your point of ‘simple birth’ contrasted to ‘simple citizenship’ other than a splitting of hairs or perhaps at most an addition of precision where none was really needed since Donofrio is not writing statute but merely drawing attention of the rule of ‘statutory construction’ to lay readers as a rule that every lawyer knows well as a basic of law.