Actually your perception isn't all correct. Late Cretaceous larger teropds, mainly Tiranosauridae (Albertosaurus, Tarbosaurus, Nanotyrannus, T-Rex) only had two claws, all other major groups of large teropds had three clwas, except for the case of the Carnotaurus and other relatives of this early cretaceous creature.
I don't know of any two claw raptor, the truth is raptors used there claws almost like we use our hands, they were very important when capturing their prey, so 3 claws would work better than 2 since they needed a third to grab hold of their "lunch".
I'm not saying it's not possible, I'm only an amateur paleontologist but I've never heard of a two-clawed raptor. So there is a mistake, it's not a production mistake, or something like that, it probably has something to do with the team in charge of the dino's anatomy, if there is one, as we all know the lbt doesn't care much for physical accuracy, if so Littlefoot's neck would never go so high and his head would be flat. =P
Just because they meant to have a two clawed raptor, if such creature never existed, it's a mistake one way or the other, it's a mere question of semantics.