The man Grey sent flying soon got in the middle of the duo Grey was aiming to kill. They were both Multi Elementalists and the most difficult to deal with, so Grey wanted to use the element of surprise to take out one, or both if possible. While sending the man flying, he had already prepared a chaos orb that had more space essence within it.
He switched places with the man the second the man got to the spot he wanted. The movement of the man didn't spot, rather, he continued moving forward, towards the direction of the single Elementalist that was on the other side.
Grey's plan was simple, kill one or both Multi Elementalists, and also use the momentum to kill the single Elementalist as well.
None of them saw Grey's switch coming, the second Grey switched with the man, he attacked the Multi Elementalist that had both the fire and earth elements. The one with the wind element might be able to react quickly, but this one wouldn't.