Tesla stock price has been gradually increasing the last week or so in anticipation of the event, so the event has already been "priced in." Further, the FOMC (fed) recently scared the market, because interest rates may be rising some time in the future (September? December? who knows), causing people to switch from investing in equities (stocks) into treasury bills. In short, this information was already anticipated but it also had to fight the FOMC announcement.