His arm wasn't raised it was pointed at the floor. It also wasn't at head height. The Tunisian literally ducks into it.
Foolish from Walker, yes, but poor refing to give it and worse to do so without consulting the available VAR.
Are you for real? I suggest you go watch a video of the incident again. The Tunisian player was looking at the ball. Walker swung his arm back with intent. Look at his face, he knew exactly what he was doing.
Poor refing? Oh, please. It was the correct call. Why would he need to consult the VAR? Besides, if it was the wrong call the VAR would have alerted him, that's how it works.