The arm was bending upwards as you'd have a broken arm in a sling, it wasn't pressed tightly on the body, the elbow maybe was touching the body but the rest of the forearm was at an angle to the stomach area.
My instant thought was football expects an offense here, I got no complaints from anyone.
The LOTG say it isn't an offense where the ball hitting the hand is a result of the hand being in a position that is natural for the movement being made. In this case I'd say if I were jumping my arm would never be pressed against my body, for balance I'd always have my arms sticking out to some degree. But it looks totally wrong not penalising someone who has their arms stuck out, jumping and blocking a shot with said arms.
Sounds like no offence based on what you've described.
The new handball law considerations are:
Deliberate - hard sell here at lower levels of football - the pros are good at disguising deliberate actions lower down not so much.
Making themselves unnaturally bigger - forearm across stomach, with elbow close to if not quite touching the side, doesn't shout to me that the player has made themselves unnaturally bigger, whilst it might look "unnatural" or awkward, it's almost like the player has done the opposite and tried to keep arms in a position where they haven't extended out.
The two comments I would make are:
1) Handball is a minefield - however you need to understand the law as written. You referenced their arm in your opinion as being in "an unnatural position" which is something that is not fully supported in law (almost the same as a referee saying they've sent a player off because they were "last man")
2) "What football expects" is not a substitute for applying law, it's really something to use when a situation arises that is not explicitly covered in the Laws. In this case, the Laws are clear and therefore "what football expects" should not be a consideration.
Edit: other consideration is whether the ball has hit the player when they are square on, or side on.