It wasn’t a ‘legal’ determination. There is no such thing as a ‘natural-born American citizen.’
If the AG reviewed and approved Fukino’s statement as Okubo claims, then it is a legal determination. That’s part of the AG’s job - to make legal determinations on behalf of the state. You may disagree with his opinion and a judge may ultimately overrule it, but it is still a legal determination by the state’s top attorney.