That's an urban myth. A child born to American citizens overseas is an American citizen from birth and qualifies for the Presidency.
There are only two classes of American citizen- natural-born and naturalized. If you are not a naturalized citizen, then you are natural-born. There is no third category of "citizen from birth, but not natural-born."
I was pretty miffed at the clown that told some mother that her daughter could not be president because she was born accross the border in Canada, even though they actually lived in the U.S and ARE U.S. citizens.