He didn't win. The option to discard your entire hand carries a requirement that you immediately draw replacement cards. You must obey the entire sentence. The two events happen in a sequence, but both must happen before anything else can occur.-- Andy
Thank, Andy. You save me the trouble of doing research about the issue :-). I'll assume that the general principle is: you cannot declare a win while the most recent card played or invoked is being resolved.
(I say "most recent" because cards like D3P2 and D2&U result in playing several more cards. If you play D2&U and then play a Keeper that fulfills a goal, you don't have to play the second card you drew before declaring the win.)