It's more like calling an articulated robot with a manipulator a 'robotic arm', despite being infinitely simpler than a human arm and with much more limited functionality.
I agree that the speed comparison seems like a very misguided metric though.
Well, it's a robot in the shape of an arm. A robotic dog doesn't have to look or behave much like a dog to earn its name.
You wouldn't call them artificial dogs nor artificial arms (unless they were being used as a prosthetic I guess, but then it's just a robotic prostethic arm)
I agree that the speed comparison seems like a very misguided metric though.