Hmmm...
Velocity :
http://lucy.allakhazam.com/spellhist...70&source=Live
SoW :
http://lucy.allakhazam.com/spellhist...78&source=Live
Looks like Velocity is 60% @ 60 and sow is 55% @ 50... The only reason mage pets are "much faster than sow" is when its an epic pet with velocity which.. this is an earth pet.
I would guess that strafing / pet root animations would account for Nizzarr pulling away from the pet.