A natural born citizen, would not be a citizen of any other nation than the United States. That is what "natural born" means. That is simply false. Stop saying it. "Natural born citizen" means a U.S. citizen at birth, i.e., not requiring naturalization. Dual citizenship has no bearing.
Not my quote. You better go complain to the guys at Right Side News to quit saying it. I doubt they'd listen to you. However, you may not have understood what they are saying. That statement you italicized has nothing to do with a naturalized citizen. It simply says you cannot be a citizen of another county and be defined as natural born in accordance with the U.S. Constitution.
BTW, I have the same opinion as Leo Donofrio on what a 'natural born citizen' is. And Donofrio has a case, docket 08A407, that will be discuss by the Supreme Court on December 5th.