I saw that wall. It's kind of ridiculous. Don't multi-millionaires have more fun things to do than flash monster-sized bitcoin walls?
That wasn't a wall of bitcoins. It was a wall of USD.
Saw the same thing yesterday. An offer to buy 1000 coins appears out of the blue and vanishes seconds later.
Same person or group?
These are possibly Virtu, Convergex, and KCG (COIN ETF Authorized Participants) testing out their buying process prior to launch. The ETF only accepts "Baskets" of 1,000 BTC minimum in exchange for COIN shares to sell.