Big banks are daily trading currencies for speculations and profit making just like us.
However there is a difference between the bank trader and a retail trader.
Bank trader trade the market in a much different as compared to us retail traders.
First major difference is there orders are much bigger than our.
Second major difference is there use of neural networks and artificial intelligence on a much bigger level.
Most big banks have shifted to algorithmic trading from manual trading.
Recently a rogue algorithm was blamed for the British Pound Flash Crash.
It is very much possible that rogue algorithm was trading for a big bank.
Size of the trade opened is one indication that confirms this suspicion.