My childhood friend who was born in Germany (dad was USAF) was told he was not eligible to be President because of the circumstances of his birth. Citizen in every other way.
Diplomats are the only exception as they carry American “soil” in a legal sense with them.
I'm guessing your friend misunderstood the law. The last two of our six are in the same situation, and the only things keeping them from being eligible is age. And temperament - #5 is too goofy and #6 would really prefer to be dictator instead. But they are absolutely NBC.