“One criterion for a person to be a natural born citizen in the USA is that both parents mush be full USA citizens at the time that a person is born.”
You are absolutely correct and it is actually the only criteria.
You may be correct. But I have a reservation that it is the only criterion. I am not up to speed on modern citizenship laws. But if your full USA parents are traveling through a foreign country when you are born for example, then the citizenship laws of that foreign country may complicate your citizenship status in the USA.