Sissoko punished because of where his arm was. I personally don't know what the answer to handball is. I had a heated debate with an Arsenal fan who said that the rule should be simplified for the referee by saying any time the ball hits hand/arm its a penalty. I believe, if that was the rule, there would be 10 pens a game as attackers would chip the ball at defenders arms.
The natural silhouette doesn't work for me either as it's too vague, arms are used for balance and for propulsion. I guess it comes back to deliberate or not.
Also from my reading this rule will not apply to handballs outside of the area. So therefore the rules are inconsistent. So if Sissoko or Rose has been outside the area no free kick would be given. Crazy