That has nothing to do with how the law itself should be interpreted.
I think his point is that if the birth certificate is fraudulent, we have no way of knowing anything about him, including whether or not he was even born here.
There is some circumstantial evidence to indicate he may have been born in Canada, and ordinarily this wouldn't overcome the perceived credibility given to a state and it's official documents, but Hawaii is unique, I believe, in that it is a state that will grant a birth certificate to the children of residents, even if those children were not born in Hawaii.
So far as I know, it is the only state in the Union that will do this, and this makes what appears to be a fake birth certificate all the more significant.