system
A chat on subreddit /r/wallstreetbets
human
Actually, that 20% drop was retailing selling. If you look at the institutional investor transaction history, there were no significant shifts at that time.  
  
 It was from a series of downgrades which retail sellers reacted immediately. Tutes don't just go dumping on analyst recommendations.  
  
 Same as the pump that happened from a $50 ROKU to a $180 Roku. It was done by a series of upgrades which retail buyers jumped in on. Tutes came afterwards

gpt
ROKU has \~85 million shares outstanding. Tutes own(ed) \~75% of those shares, as of last qtr. The stock dropped 20%+, trading upwards of 65 million shares in one day. 
  
 Hint: All of the 13F filings are  not available/filed yet. I'm not seeing MS,Blackrock,WF, or any of the other (former) large owners of ROKU.