I would have to say that this move is highly unusual, but looking at a few factors it kind of makes sense.
1. Even with the news the SPX is only down 1.1% today. A VIX of 16 prices in an expectation of about a 1% move on any given day over the next 30 days, so we are within that range.
2. The VIX was rising into the announcement, so I think some of this move was priced in. Believe me, when we got the rally of the lows this morning the VIX and the VIX futures got smoked, so there were many market players looking to dump some long vol exposure.
3. The SPX is still well above technical support levels and really has just found its way back to the recent mean of 1350.
4. Plus Sept futures holding a substantial premium to cash, indicates back month vol firm.
5. The largest open interest strike for august options in the VIX is 18, this coupled with august including laborday in its September calculation, could put downward pressure on the Vix into 18