I don't see this kid as necessarily discredited. He got word that the C's hopes were up--which by all accounts they were--and that it was for a two-year deal (which, it turns out, it likely was).
As to Horford, he also projected that Al would make it official at the close of the Durant meeting--and that's what he seems to have done.
Sure, the kid could have been blowing smoke, but a careful reading of his tweets doesn't actually outright discredit him.