Once that buy order was filled, the remaining bid/ask prices remained the same. That would happen every time unless it cleared off the sell wall, or there was a bid above 808
No.
I was sitting watching this as it happened. For a big like that to go through on the exchange in the normal manner, it would either have to bite a big chunk away from the Bid or Ask walls. This didn't. It was as though a large buyer and seller magically approached the market at the same time and met each others demands to the tune of 800 BTC. Bid/Ask depth remained constant throughout.
Yet more fishy dodgy shite from exchanges that I really have trouble feeling that I can trust.