Honestly, if you don't know that CNBC is to the financial markets as what the Hee Haw is to the news, then I can't help you.
CNBC does NOT know what the cause of this was. The exchanges will come out with some "computer glitch" story or the "fat finger" excuse, but neither of those are true. FWIW, the fat finger excuse is, in a nutshell, some trader accidentally pressing the wrong button on the trading desk.
The market was at a technical support level with various moving averages, timelines, etc. all coming into play. Many people had/have stop losses because the market was/is looking due for a correction. Algo/HFT pounced on this, collectively, and thus the massive drop.
Trust me, if you are buying into what CNBC tells you, you are really missing the truth...