After several days of selling the S&P500 and other stock markets gamma squeeze higher. It appears to be a gamma squeeze play as options dealers were most likely forced to buy back short hedges. As implied volatility (e.g. VIX) goes down and put options are sold the delta of out of the money put options decreases (vanna). This means that dealers are over-hedged and will buy back those hedges. This pushes the equity market up, which leads to lower implied volatility, more puts being sold, and more dealer (stock) buying.