Blizzard was most likely planning to reveal the Switch version of Diablo 3 at Blizz Con this November, but the overzealous Forbes editors wanted to share the news way to early. Of course, Forbes already deleted the article, but it was too late... no one can really delete anything from the Internet. The article reveals the name of the Switch version, as well as the exclusives that come with it.
https://www.notebookcheck.net/Diablo-3-is-coming-to-the-Nintendo-Switch.323346.0.html
Today it was officially announced by both Blizzard and Nintendo.
So this is one of the "multiple" Diablo projects. It remains to be seen what other (others, hopefully) reveals we'll get at Gamescom and/or Blizzcon.