I don't know about their situation, but US Citizenship doesn't pass down from parent to child in an unlimited way (though it is often thought to).

https://en.wikipedia.org/wiki/United_States_nationality_law#...

If you're born abroad to a single citizen parent, that citizen parent must have lived in the US for at least 5 years total and at least 2 years after the citizen parent's 14th birthday. If the citizen parent doesn't satisfy that when you're born, you don't qualify for birthright citizenship.

So, the US requires a substantial period of residence prior to the child's birth in order to pass down citizenship to the child.