Obvious hoax, and I think it just confirms how not a big deal Twitter is that the Bowie camp doesn't even feel the need to comment.
I think what Adam was talking about - him confirming or denying working on new material - is exactly why he isn't commenting. And I think that's also a good indication that he is not working on new material. Since when has Bowie not wanted buzz behind an album?
Conversely, there's some slim silver lining in the fact that he hasn't denied working on new material (either in response to this or otherwise) - obviously he isn't, but letting it remain ambiguous helps him maintain a little bit more fan interest. If he still cares about fan interest, maybe he is still thinking about doing a new album in the future. Or at least wants to keep the option open.
But at this point, I do feel it's likely that Bowie is done.
Non importa quanto si aspetta,ma chi si aspetta.