What do they do with bodies that are facing backwards? Is there a little side channel that flips them around? Nope, they just get tossed back into the hopper to try again. It's effectively random which way they'll be facing when they get picked up, so they'll eventually get through.
I thought that was a nice illustration of keeping things simple and taking advantage of processes you already have, and seems similar in spirit to this.
Just a remark from a Lego nerd: it's attaching arms to bodies, not heads. The neck has a stripe on the front, so that is where the camera looks at to determine which side is facing up.
Maybe there's some defective minifig body with a mechanical flaw that causes it to always get picked up facing backwards, that's spent years being picked up and rejected over and over.