Yes, either that page was wrong or misleading or I was reading it incorrectly. Yet, while most nationals are residents of outlying possessions, the law has curious corners.
Section 308 of the Immigration and Nationality Act:
Unless otherwise provided in section 301 of this title, the following shall be nationals, but not citizens of the United States at birth:
(1) A person born in an outlying possession of the United States on or after the date of formal acquisition of such possession;
(2) A person born outside the United States and is outlying possessions of parents both of whom are nationals, but not citizens, of the United States, and have had a residence in the United States, or one of its outlying possessions prior to the birth of such person;
(3) A person of unknown parentage found in an outlying possession of the United States while under the age of five years, until shown, prior to attaining the age of twenty-one years, not to have been born in such outlying possessions; and
(4) A person born outside the United States and its outlying possessions of parents one of whom is an alien, and the other a national, but not a citizen, of the United States who, prior to the birth of such person, was physically present in the United States or its outlying possessions for a period or periods totaling not less than seven years in any continuous period of ten years -
(A) during which the national parent was not outside the United States or its outlying possessions for a continuous period of more than one year, and
(B) at least five years of which were after attaining the age of fourteen years.
Again if I am reading this correctly, section (4) allows for some people not born on U.S. soil to be termed nationals without residency on outlying possessions. Otherwise the term nationals does appear to be limited to residents of outlying possessions.
The status and attitude of people in the outlying possessions was interestingly handled in Doug Mack’s The Not-Quite States of America: Dispatches from the Territories and Other Far-Flung Outposts of the USA. Mack is a travel writer who - like unfortunately most of us - realized he knew nothing about America’s possessions. So he set off to travel to every one and talk to the people there. Light reading, not scholarly research, but it hit me in the heart of my own ignorance.