I have no idea what it is. Maybe they have movement speed traits or speed-based equipped; regardless, once I realized it it quickly sucked the fun out of the game. I watched a thief run easily ahead of the rest of the pack, and consistently score 1st or 2nd, and it strikes me as the work of Signet of Shadows. It was hard to tell since he got ahead of me so easily, but I also got the impression that he was shadowstepping, although he could have just been using the sprint ability.
If I’m wrong, please correct me, but I didn’t know I was going to have to build specifically for the race in order to enjoy it… particularly with skills that I don’t even have access to as a Guardian.