The corona might of caused the stock markets to crash which might of caused the price of BTC to go from $8000 to $6000, what happened afterwards was due to massive long liquidations on Bitmex.

Being the largest derivatives exchange and basically bitcoin hovering around $10000 back in Feb 2020, made people open up massive long positions due to the halving FOMO. And the problem with being long with BTC as collateral is that if BTC goes down, your collateral also goes down. So even if you were 1x long at $8000, you would of been liquidated anyways at $4000. And there were maybe >$1 billion of these liquidations, hence why it crashed down to $3500.

This is the issue with high leverage derivative markets on a thin orderbook.