Clearly, Sentabale did not proactively brief the media about filing their claim - if they had done so it would have been when they filed it, on 23 March. Also, the Reuters report specifically states their source for the information: “According to a record made public on Friday, Sentebale lodged a defamation claim last month at the High Court against Harry and one of his close friends, Mark Dyer, who was also a trustee of the charity”
And did you not read my earlier post? The document Sentabale have filed at this stage is likely just a claim form which gives very limited details of the claim.