Nope, someone getting violently stopped out.
The same thing happened in a couple of ETFs I track - they traded down 15%-20% this morning when the underlying stock baskets were only down 4%-5%. (They came back surprisingly quickly, though - the dislocations lasted about 15 minutes, tops. If I hadn't been woken up by a garbage truck at 4:30 this morning I would've slept through the whole thing, but for those 15 minutes there was free cash lying on the street.)
Basically what happened is this:
- The market-makers switched their machines off because markets were unusually volatile;
- Price-insensitive retail traders said to their brokers "oh my god get me out at any price" - or, equivalently, their brokers said "you've lost too much money, we're cutting you out";
- Those retail traders were forcibly sold out, into a market where prices were plunging and there was no liquidity;
- Prices end up plunging miles away from their fair value until the market-makers switch their machines back on (or smart traders buy the dislocated ETFs and wait for them to converge.)
The buried lede here is that ETFs work quite well! Stuff swung around a bit for about 15 minutes, but if you weren't using leverage - if you were just buying-and-holding - and you were off doing your job or something like that, then as far as you were concerned the ETF tracked the basket of stocks very nicely.