It was clearly not "deliberate" so the question is whether he "made their body unnaturally bigger." That's a judgment call, but I can see how the ref saw it as natural.

It is an offence if a player:

• deliberately touches the ball with their hand/arm, for example moving the hand/arm towards the ball

• touches the ball with their hand/arm when it has made their body unnaturally bigger. A player is considered to have made their body unnaturally bigger when the position of their hand/arm is not a consequence of, or justifiable by, the player’s body movement for that specific situation. By having their hand/arm in such a position, the player takes a risk of their hand/arm being hit by the ball and being penalised

• scores in the opponents’ goal:

  • directly from their hand/arm, even if accidental, including by the goalkeeper

  • immediately after the ball has touched their hand/arm, even if accidental