IIRC, Disney wanted the writer to sign an NDA before they'd even negotiate to pay him what they owe. So giving their silence the benefit of the doubt now goes beyond charity and firmly into idiocy.
Has the writer posted the text of the contract somewhere? Is the text of the contract under NDA? I am asking because media companies (film, music, anything really) screwing over artists in contracts is fairly commonplace. Them ignoring contracts altogether and just doing whatever is not something I had heard of before. In the absence of other information, I lean towards believing they had snuck a term into the artist's contract allowing them to do what they have done here, because that's their MO. If you think that makes me an idiot, so be it.
