Running "with" a dog, which many races allow, is and should be considered entirely different from canicross, which can take minutes off of your best time if you're running behind a good dog. The problem is that even if you're only intending to run "with" your dog, it's very hard to ensure that you don't receive any assistance at all. I think it's cool that races let people run with dogs, but they should explicitly clarify that anything more than incidental assistance isn't allowed and you should be ineligible for prizes.
As for the OP, I'm highly skeptical that a lab helped anyone run a 10-miler faster than they otherwise would have. Canicross dogs are pretty specialized--usually designer mixes of shorthaired hunting dogs and sled dogs. Labs are pretty poor runners. Even if it tore off like crazy for the first mile, it was probably not doing any pulling for most of the race. You really shouldn't even run a lab that far.