That is not true, he could be a natural born citizen even if he was born out of the States. Again, I'm not saying that he is, but he could be. Natural born citizen is not the same as native born citizen. A native born citizen is someone born within United States territory, and thus a citizen by birth by jus soli (i.e. the right of soil). Someone can also be a citizen by birth by jos sanguinis (i.e. the right of blood). Both of those are considered natural born citizens. Although there has never been a specific Supreme Court ruling defining what natural born citizen means for constitutional purposes, U.S. code defines citizens and citizens at birth, with the later being generally regarded as natural born citizens.
If someone had to be born in the States to be a natural born citizen then John McCain would not be a natural born citizen, as he was born outside of the States. Under U.S. Code however, he is a citizen at birth. Congress passed a resolution specifically recognizing that he was indeed a natural born citizen, in which they recognized that some persons born outside of the United States had previously been considered eligible to the Presidency. Ironically, Obama (as well as Clinton) was a sponsor of that resolution. That resolution didn't make John McCain a natural born citizen, it merely recognized that he was one.