I was watching the sell wall, and it built up to 12,000 slowly over the period of at least 45 minutes, probably because the ticker price said $8499 on Coinbase.

Where this all starts to smell a little funny is how badly and strangely this was rolled out, how they allowed some trades, and how the price crept up 50-100% before the announcement. Someone said they accidentally released some bitcoin cash UI feature that tipped people off a few days ago. More incompetence.