If it's a new car, the engine should never be making a "loud growl sound" and should never sputter at idle. You should take it back in if no other reason, because of that whether it's related to the oil being overfilled or not.
First, several things can happen in an overfilled oil scenario:
- Your crank is whipping the oil up so that it becomes mostly air, causing improper lubrication of the engine components and potential damage to the oil pump. Yours was definitely overfilled to the point this was happening! But, that doesn't necessarily mean the pump or other components were damaged.
- When the engine is grossly over-filled (like it was in your case), it can make it to the exhaust track and it will wreak havoc on your catalytic coverts and potentially cause issues to censors in your exhaust system. This often shows up on a scan, assuming they did one -- which is unlikely according to my personal experience with this stuff.
- If it gets into the combustion chamber, passed the oil rings it can cause plugs to fowl - you were definitely burning the oil as evidenced by the black smoke.
Of course, none of this is good for your engine. But, you did not drive very far or very fast. That's good as more severe issues like bent rod etc. are unlikely to have occurred -- also this would probably be obvious to you later if it had as you'd be hearing knocking and having rough idle etc. It concerns me that you do have a rough idle.
To say the least, you should take it back and start holding them accountable. Tell them it isn't running right and is making noises on occasion. If it were me, I would demand a complete diagnostic be done including checking the oil pressure at different RPMs, engine timing, and of course running a complete scan for codes. Every time I've heard of this happening, the culprits will try to blow you off and say it doesn't cause damage - that is not always true! Demand they scan it and show you the results. They should not charge you for any of this. But, if you feel as though they are blowing you off -- likely to happen in my experience -- go somewhere else, explain the scenario and pay for the diagnostic work only.
Keep in mind that not all dealerships have very experienced techs. My experience, more often than not is that the dealership is about on par with pep-boys or worse. Don't take their word for anything. The fact that it was overfilled is already proof they are careless amateurs. I would be preparing for a lawsuit.