Yes, but that is a very special case; with a central bank pegging a currency, any trades there were quite risky by nature. And the flash crash did not happen in one second, but the market slid down gradually until it went into freefall, and news-related crashes still fill close by orders (stops that should be there for emergency purposes) and only get unstable after the initial substantial fall. My point is, a 3 sigma event in liquid futures will not impact a day trader with the same type of risk of loss that it will impact someone with a position trade on who has no stop protection in place. Now, single stocks, which can be halted for many reasons and all at the discretion of an exchange, even for day trades provide a quite substantial risk, as thousands can be lost with no way to exit the position unless it is already hedged with options or some other means.
At any rate, I was in no way encouraging using high leverage, and recommend against doing so.