“Handball is the illegal contact/touch of the ball with the hand(s) and/or arm(s). However, it is not automatically a handball offence every time the ball touches a player’s hand/arm.

A handball offence is when a player (except the goalkeeper in their own penalty area):

-deliberately touches the ball with their hand/arm
touches the ball with their hand/arm when it -is in a position that makes their body unnaturally bigger and when that position is not the result of their body moving fairly as part of play
-scores a goal against the other team with their hand/arm or scores immediately after the ball touches their hand/arm (even if the touch was accidental)”

It was not deliberate. His back was turned.
The arm did not make the body bigger. In fact with the elbow pulled into the body like that it was the opposite.
It did not lead to or prevent a goal.

Just a strange decision.