Except that's not true and the data entry for the giant mudcrab is not the equivalent to a normal mudcrab. It's not just scaled up, it's stronger too.
The NPCs should make different actions depending on different entries that triggers their AI.
They do react differently to different entitites. This is a mudcrab, so they treat it like a mudcrab. With the CK you could change mudcrabs to create the reactions that dragons get. Even if it is a giant mudcrab, it's pretty damned obvious, with the video as evidence, that the NPCs simply percieve it as being a mudcrab.