Zach mentioned that at least some of the BitFury gear was installed and running during the AMA. It is possible that he is paying out coin earned by that hardware over the last couple (or more) weeks. NB: Previous comment is SPECULATION. He has not indicated to me that that is the case. But it does make sense.
grnbrg.
I would concur that a bit of a "balloon" payment makes sense for the first bonus. Guess we will have to see a few weeks worth to see what it's averaging.