I remember the day pretty clearly. Bids went bananas during the sell off which happens at like 2pm. By 4pm most of the market had recovered but Spx options wer still trading 15 handles wide (compared to 30 cents in the institutional space). I believe that the feb event was completely different in that it was extremely isolated. A very specific part of the market (vix and options that affect the vix level) got dislocated and everything else was pretty unchanged. A long short trader could have completely missed the entire 24 hours. A single stock vol trader would have barely noticed it. The flash crash was much more encompassing and frankly was a lot scarier. I remember having an all hands meeting to discuss rumors that it was financial terrorism.