Its hard to know for sure because of the very short amount of footage we've seen, but the baby tuskarr's arms are held lower, more like the Vulpera model than the Pigmy model. I think the Baby Tuskaar is the pre-order pet.
Models don't need to be exactly the same to share rigging: For Example, Nightborne are skinnier than Night elves, Kul'Tirans are much bulkier than Zandalari.