I don’t know where you read this. But nobody who writes this, or says this, believes it.
It is simply a lie, an intentional, knowing lie.
It is, of course, pure, unadulterated racism. What’s really being said is not that Senator Harris is barred from the office of the presidency because of her parents’ birth, but that she is barred because she is Black.
That’s it. That’s all there is to it. There is no other possible interpretation. Nobody believes it. Nobody. Those who say, or write, it are doing so because they can’t get away with saying that a Black person should not, or cannot, be president. They think they’ve found a way to say exactly that in more polite language.
That said, given our current president’s track record, I wouldn’t be surprised to hear it from him, or from surrogates. He said it about Barack Obama, and he said it about Ted Cruz. I fully expect him to spout the same lie during this campaign.