It will be a source but IMO it is not a big enough source to cycle as fast as you have done, unless your Live Rock was not only cured but already cycled. This would require the place you bought the rock from to maintain the cycle with a decent sized bio load and then have little to no die off from when you transported it from the store to your tank.
Again, I'll let the experts correct me.
If you didn't have any coral or invertebrates in your tank, I would have suggested dosing the tank with 2-4ppm of ammonia and seeing it the tank was able to convert that to nitrates over night...but since you have added coral, I wouldn't recommend that.