Read the article to understand why he concludes that. This isn't just an internet "commentator", he's a highly respected lawyer. There's a lot of research and quote attribution, good discussion, etc. He also goes out of his way to say those who disagree aren't nuts, and clearly says the term "birther" was made up as a pejorative term.
Try reading it instead of criticizing first.
Try reading it instead of criticizing first. I may criticize any incorrect statement whenever and wherever it appears. I needn't show a hall pass endorsed by you, to the effect that I've read Blackstone in full, before venturing an opinion on the grounds hazarded by this or any other writer.