It had to have been Institutional money but with the help of retail, unbeknownst to them.
If I were to guess how Softbank's hedgefund went about this play, they noticed the extremely high level of call buying in large cap tech (retail & institutions) over the past few months and some smartass drewup a play to gamma squeeze the dealers. There were many factors at play, a key one being that AAPL & TSLA were running low on float.
I'm guessing once the cat got out of the bag, softbank or whoever starts unloading their calls, and dealers correspondingly sell the underlying. As a proxy, you can see this in the volume of QQQ sold last 3 trading days.
This does not necessarily mark the top for the markets, because there wasn't any price discovery in the process, but if this phenomenon is over, we should see a cooloff in the parabolic runs in those names.
From a stock market standpoint, 2020 will be remembered for how the Options market changed the game.