I will just chalk anything like this up to non-canon attempt at money making. To me it is no different than if someone said they were writing a sequel to Dante's Inferno or or Hemingway's The Sun Also Rises.
Apparently, according to the article, the author feels the same way. It claims he won't be trying to write as Douglas Adams, but will be writing his own book, using the Adams characters and setting.
I don't think this was needed, in any way, shape, or form, but at least they're being straightforward about it.
The author says, in reaction to being chosen by the Adams Estate for this project, that it's like being offered the superpower of his choice. I haven't read any of his stuff, but that's a fine, geeky sentiment to have, and for that I have to approve.
I wonder if this will expand on the stuff in Salmon of Doubt, or if this will go off on its' own direction? The unfinished story in Salmon was supposed to be the direction Douglas Adams was planning to take for the next, and really really real final Hitchiker's book.