Oh, I saw that the two dissenters cited de Vattel (once) in their dissent. They didn't convince the other six Justices in 1898, and 103 years later, they haven't convinced any Judges or Justices, seeing as how every birther lawsuit has failed.
If not "understand[ing] why the comment...is UNQUESTIONABLY not a binding precedent" puts me in the company of Judge Brown rather than you, I'm happy to be in her company.
And you still can't answer why five Justices, none of whom was appointed by allegedly illegitimate President Arthur, joined Justice Gray's opinion in Wong Kim Ark. Two Justices dissented, but none of the five who joined the majority opinion wrote concurring or separate opinions.
(You also can't explain why on Earth Justice Gray would "protect" a President who had been dead for twelve years by the time Wong Kim Ark was decided. Don't forget that Congress has to CONFIRM appointees...how far do you want to take your conspiracy theory?)