What you saw was Swamp Gas!! I suspect this was a "because they can" gap fill/bottom test in advance of a big USD up move?
Geitner forgot he was at the G-20 meeting and was using 100,000,0000 bills to wipe his ass, light his cuban cigars, and start fires to roast smores over. Realizing his faux paux, he quickly reiterated his strong dollar policy and simealtaneously printed 500,000,000,000 on his portable HP fed reserve dollar printer and bought 1,500,000,000,000 worth of treasurty bonds from his iSwifttrade brokerage account. Whew...
Most probably nothing as this is the futures contract and not the index itself. Probably one algo or market order bad trade when there was no liquidity and everyone was sipping wine at the bar.