The conclusion confused me for a moment David, but then I remembered something.
Why was a copy sent to "W. H. Smith"?
"W. H. Smith", I presume, is William Henry Smith, the owner of the chain of book stalls/newspaper stands that became the center of a publishing firm. He was also a Tory politician, best recalled now as the basis (when Disraeli made him First Lord of the Admiralty in the 1870s) for William S. Gilbert's "Sir Joseph Porter" in the libretto of "HMS Pinafore". A stolid and steady and honest man, he was known as "Old Probity" in the House of Commons.
When Salisbury became Prime Minister in 1885, he had a problem. He was a Marquis, and sat in the House of Lords, but the basis of real political power and debate in English democracy was the House of Commons. He could have done what Lord Home did in the 1960s, resigned his title, and taken a seat in Commons in a special election, but it wasn't considered a realistic type of move in the 1880s. So Salisbury chose to have some leading Tory in the House for his Commons leader while he was Prime Minister. In his second ministry (that is by 1888), Salisbury was using W.H. Smith for this role. The report had to be sent to the Commons leader when it was ready, and Smith (after he read it) presumably sent it on to (or discussed it with) Salisbury.
Although, one would think Lord Salisbury would have also heard of it from Matthews.