Both mothers moved to the United States as children and lived in the United States for at least 10 years prior to birthing their children. It's pretty reasonable to assume these women naturalized, especially under the marriage/citizenship laws at the time, which made it automatic. These women were permanent U.S. residents and apparently lived here as citizens. By contrast, Obama's father did not stay in the United States. Obama's mama did not stay in the United States. Obama did not stay in the United States, although he did return later. At best, this would mean any allegiance Obama had to the United States had to skip a generation since he ended up being raised by his grandparents. It's not even close to being the same as Hoover or Wilson.
OK, so to you, an NBC does not mean born in the US of NBC parents, correct?