Look at it this way:
If you are born and you are a citizen, then are you an alien? No. You are NOT an alien if you are born a citizen (citizen at birth).
If you are born and you are a citizen, are you a naturalized citizen? No. No. You are NOT a naturalized citizen if you are born a citizen (citizen at birth).
If you are born and you are a citizen, are you a natural born citizen? Yes.
No. Absolutely not.
A native born citizen is one who is born in the United States.
A natural born citizen is one born in the United States to parents who are citizens of the United States
It’s really rather simple.