Keep in mind Mumper stated the following on twitter...
"Stunted Direhorn is not 5.2 anymore, most likely 5.3 at this point. We have a cool replacement though!"
It's possible the other Direhorn pets may be the replacements he mentions.
True. But that seems odd to me.
Look at the various saber cubs or raptor hatchlings. All the same model, just with different skins. If one Direhorn isn't ready for 5.2, I can't see why the others would be unless the team working on the pets started with those first.