At the time of his birth one parent was not an American citizen. Also there was doubt that he himself was born in the US and not Canada.
So what? I wasn't a US Citizen either when my son was born in Germany in March of 1963 and my daughter in 1970. My husband registered them both with the American Consulate in Munich, Germany when they were 6 weeks old. Both were born in the same US Army hospital, which means they were born on US soil.
You don't really think they would have gotten American birth certificates and American Passports issued if they had not qualified? Get real and stop it with the birther nonesense.