I mentioned in the other thread, I reckon it is something coached to be called as a alternative play if they notice it as the players were standing in coached positions and a quick hand signal wouldn't have meant much to Digne unless he was aware what it meant. But the lead tactic was to put the ball in the 6 yard box apart from their defender was having a blinder and was probably their MOTM and almost full MOTM even with the goals, which he could do nothing about.
I agree that wasn't an 'off the cuff' set piece, it felt much more like as a "when the situation presents itself" set piece. Unlike the corners, there was only one West Ham player looking at Sancho, Digne and SJM on the edge of the box (at corners, it was two West Ham players covering those three), so I think they knew they could give one of them a free shot at goal from a decent position. I definitely agree that it was Sancho that saw it, and called it, but everyone from Cash onwards knew what to do. I suspect that if the free West Ham defender had charged directly in Sancho's direction, it would have been Digne with the shot.
I suspect Rogers reaction, the "why haven't you crossed it?" arms, was due to the fact we were actually getting a lot of joy dropping it right on the keepers head, so he probably thought we should keep doing the same (reasonable enough).