I've heard various definitions requiring anything from one parent a US citizen with the child born anywhere in the world to both parents citizens with the child born on US soil, but I have no idea which (if any) is the real definition.
Well, he would not be a US Citizen if he wasn’t born on US soil because his mother was not old enough to transfer citizenship to us.
He also would not be a “Natural Born Citizen” if he was to have to be naturalized later on.
I may be incorrect in him not being a “US Citizen”, but I just think that sounds more outrageous and will cause people to think “Oh, they are nuts”. We need to focus on the specifics of “Natural Born” for the office of President and then maybe people won’t just arbitrarily dismiss it.