It's in the conclusion of the opinion.
"...it is expressly agreed that his residence has always been in the United States, and not elsewhere; that each of his temporary visits to China, the one for some months when he was about seventeen years old, and the other for something like a year about the time of his coming of age, was made with the intention of returning, and was followed by his actual return, to the United States, ..."
" ...the single question stated at the beginning of this opinion, namely, whether a child born in the United States, of parent of Chinese descent, who, at the time of his birth, are subjects of the Emperor of China, but have a permanent domicil and residence in the United States, and are there carrying on business, and are not employed in any diplomatic or official capacity under the Emperor of China, becomes at the time of his birth a citizen of the United States. For the reasons above stated, this court is of opinion that the question must be answered in the affirmative."
If the only necessary factor was incidence of birth in the United States, there's no need to go on and on about the parents having permanent domicil and the child always having lived in the United States. This is important because the common law hinges on remaining within the country. Also, note that it doesn't declare the plaintiff to be a natural born citizen, but instead a 'citizen of the United States."
Below is a look at the common law citiation from Wong Km Ark, where it emphasizes that in England, children of aliens were natural born subjects if their parents remained in the country and gave allegiance to the King. This concept continued, supposably in some colonies in the United States, with citizen substituting for subject. The only contention I have is that we know some colonies only considered the children of British subjects to be natural born subjects, but not aliens.
"Such allegiance and protection were mutual -- as expressed in the maxim protectio trahit subjectionem, et subjectio protectionem -- and were not restricted to natural-born subjects and naturalized subjects, or to those who had taken an oath of allegiance, but were predicable of aliens in amity so long as they were within the kingdom. Children, born in England, of such aliens were therefore natural-born subjects."
That is the only part of what you posted that is relevant to a specific determination of citizenship status. It supports what I posted before. There final decision, based on definitions of "natural born citizenship," established in Minor v. Happersett, was that someone born of foreign citizens on U.S. soil was "native-born," as opposed to the classification of "natural-born."
I don't see how anyone can say that SCOTUS has not definitively ruled on the issue. They weren't trying to say the subjects of either case was natural-born but in the process they did define it.