Makes sense. Trump’s mother was naturalized as an American citizen in 1942, and D. Trump was born in 1946, and by then his mother already called herself American. That would make her first-gen naturalized American in the eyes of the census, and D. Trump second gen given that he was born to a naturalized immigrant.

Technicalities aside, Donald Trump was born in America to a person that just a few years earlier called herself Scottish. He should certainly know about the prevalence of immigration in America, between his own Scottish and German background, and marrying immigrants himself.