I'm just guessing here, but did the pellets produce a very heavy white smoke that didn't last long? What you have on your CB is what we call creosote...it comes from a continuous heavy white smoke or choked-off ventilation. BTW, this will likely result in a bitter tasting smoke on the food.
If I may suggest, for the future: you need to control the heat and air getting to small pieces of smoke wood such as chips or pellets. By placing in a metal container such as a soup can (burned out/seasoned) and placed close to (not on/in) the fire, this will limit heat and air. You want the smoke source to smolder slowly and produce a slight but steady smoke, not burn up hot and fast like your fuel. A far better choice for smoke with a solid fuel heat source is wood chunks placed in with, or next to, your how coals. Chunks are much more forgiving, as the larger size translates to less surface area and they will burn (or as we would prefer, smolder) more slowly than small pieces.
Eric