I was clearly a 'leak' orchestrated by H&M to distract attention away from the coronation (it won't for more than a day or two) because it only benefits them. The telegraph is Team Sussex as Harry himself said on Netflix, they were the only paper that was not a tabloid, so it's clear they would leak to a 'friendly' newspaper.
The way it's done is the same as the Scobie communications for Finding Freedom, only this time there are no palace officials, or anyone else who is honest, who can produce emails pointing out meghans lies.
The shock to the Sussexes and the telegraph, is that Charles has decided 'never complain' etc has had its day and has instructed his legal team. This scenario is highly similar to the Meghan Markle and Thomas Markle court case regarding private correspondence, where Thomas lost for leaking. I'm sure H&M have played it at a very long arms length and it won't come back on them.
The Sussex's have instructed their own legal team, but as lawyers simply do as they're told, nothing will come to light. The telegraph itself has rowed back on its claims in later updates, and the 'journalist' is a pro H&M reporter as evidenced by her puff piece re the Sentebale charity and the Sussex squad...with a nice picture of Harry and an African child.