@Hellonearth: Actually, those frames were flipped upside-down. Therefore, they must be a reflection of some sort. If this is true, then they are indeed reflecting the right arm

.
You don't just rotate the image of turn your head. Literally flip it vertically in MS Paint and you'll see it's the right hand.
However, if this isn't a reflection, then that's a huge error. Plus it would make people wonder "Why the heck did they need to flip that picture upside-down, anyway?" They could've just posed the Predator rightside-up with his arm in a different pose. Jeez...