If it was so common that defenders cannot control their arms in close quarters in the box there would be a handball just about every game. Defenders would have their hands up every aerial challenge and the ball will hit a hand at some point.
At some point, I suppose defenders would just start starfish leaping at opponents. After all, they can always claim they cannot know for sure before the ball is kicked that it will hit their hand. But theyare certainly increasing the odds it will and gaining a big advantage.
I'm a big hand to ball guy myself so strictly enforcing that rule I would say there is no penalty because at no point did Stephens ever intentionally play the ball or try to gain an advantage by placing his hands in a given space.
At the same time, I'd also feel like Stephens got a little lucky and got away with one. Because he definitely made himself taller by having his hands up, even if that was not his intent. And he messed up a big hill scoring opportunity. Instead he got unlucky.
I do not blame Stephens, but I also do not blame the official. It's basically an unlucky deflection to me. It just hit his hand for an unfortunate pen, instead if bouncing off a legal body part and into the goal. Six inches difference, and nothing happens.
Unlucky, yes. But we gave them too many chances so eventually something was going to happen.