If the market suppose to be down (for any reason) but it reverse in action. There is only 1 reason, speculators are luring more retail investors by giving them the uptrend illusion.
For example in QQQQ, looking at yesterday's volume after 11:00am, the volumes are very thin but the price still goes up a bit higher than what's at 11:00am. It indicates there is lack of demand. (This is the illusion for an uptrend, it's up but no more buyer)
But look at today's market, initial volume was high, and the trend is down, and the volume are high as well. This is a real trend, yesterday was a fake one.