Bitmex is the largest exchange and provides most of the liquidity for many of the traders. However BTC in Feb was over $10K and many were assuming it would hit a new ATH since the halving was approaching, hence they opened leverage positions and when it broke the $7500 area there was nothing but long liqudations after long liquidations and pretty much there was a $1 billion of long liquidations and no bidders, hence the exchange went down and as a result it saved BTC from going to $0.
There's no way Bitmex liquidations could ever bring BTC to $0, or anywhere close to it:
For prices to fall on spot exchanges, people need to sell real BTC,
on spot exchanges. Long liquidations on Bitmex do not accomplish that, and we know zero withdrawals left Bitmex during the crash because they only process withdrawals during mornings US time.
Nobody knows it was Bitmex-tied algorithms that dumped all that supply. That's just a big unproven assumption.
All we know is inflows to spot exchanges increased ~170K BTC more than usual in the days preceding the crash. Massive supply leads to lower price.
A lot of over-leveraged traders got destroyed on Bitmex, I'll agree with that. I am however not convinced Bitmex controls the spot market.
When Bitmex went down, the perpetual swap market was already a few hundred bucks below spot price. If it kept going, it would have just diverged more and more from spot prices. There wasn't that much open interest left on Bitmex after the crash anyway.