I can be a little confusing getting used to this stuff. ND is the "big" nasdaq contract... NQ is the mini contract, as you noted. The big contract, during regular trading hours, trades in the pit in Chicago, while the mini contract, during the same hours, trades on the electronic market. That's what's meant when the CME sometimes talks about "side-by-side" trading. Because the two markets are "separate", there will be small discrepancies in the prices between the two, just because there are two different groups of traders involved in each market.
Thanks