Retail investors bought $4.7 billion in stocks on Thursday, the highest level over the past decade, JPMorgan said in a note on Friday. The historic "buy-to-dip" move by retail investors included names such as Nvidia, Amazon and S&P exchange-traded funds, but they sold Tesla. Small-cap technology was one of individuals' favorite sector picks amid the meltdown, while institutional investors have increased their bets against the sector.