I think this has highlighted an interesting contradiction in the wording of the handball law - although who is surprised by that

It states that it’s a handball offence if a player handles the ball when their hand has made their body unnaturally bigger. However it then goes on to define “unnaturally bigger” as “not justifiable by their movement for that situation”.
In this instance, it’s unclear whether or not it hits the hand of the Motherwell player. Even if it does, his hand is positioned right in front of his head so it’s not made his body any bigger. Yet there’s also a reasonable argument that jumping with your hand in front of your head is not a natural way to jump.
Long and short of it, I’ve no idea and VAR should’ve stayed well clear.