Without Googling, I'm gonna guess that this means WASPy white families who came from Europe many generations ago. You know, the people who built this country.
And it does not mean black people descended from families who were brought here against their will 200 to 400 years ago to build this country. And it definitely doesn't mean anyone descended from the Chinese families who came here to build the railroads over 150 years ago. And it obviously does not include Hispanic immigrants who've been building this country, literally, for generations. It means the German, Irish, Italian, and English immigrants who built this country.
Also, if you are white and your family just got here, like, ya know, the First Lady, or Elon, you're a "Heritage American."
That about right...?