That was intended as pure satire. But the idea that Holmes was born or grew up in the United States was by no means new. "Was Sherlock Holmes an American?"by Christopher Morley appeared in Vincent Starrett's 221B: Studies in Sherlock Holmes in 1940.
More startlingly, the late John McAleer wrote an essay called "Henry David Thoreau Alias Sherlock Holmes," in which he argued that the two men were on in the same, citing as proof that "Holmes knew Thoreau's works, and looked like him, thought like him, felt like him and behaved like him."
The essay was published somewhere, as I recall, but what I have in my files is a photocopy of the typed manuscript, which John sent. I especially liked the over-the-top ending:
I could say our case is made but what is a case without a cipher? We have one. Take heed of the given names of Thoreau and Holmes. The first and second letter of Henry are duplicated in the first and third letters of Sherlock. Note the surnames. The first and second letters of Holmes are duplicated in the first and third letters of Thoreau. Put them together and we have -- He he, Ho, ho! Obviously our droll naturalist turned sleuth is having a a quiet laugh at posterity's expense. The Baconians would eat their hearts out for a cipher as invulnerable as this one.Nicely done, I say! What's your favorite far-out theory from the wonderful world of Sherlock Holmes?
I close with an affirmation that, certainly, no one will care to dispute -- Sherlock Holmes was nothing if not Thoreau!