What do you trust? They owners manual that says 6 qts, the oil you poured in that said 6 qts or the dipstick that says over full? Me I don't trust the dipstick if I know I took out 6 qts, 6 are going back in no matter if the dipstick says it over full.
Several things could have happened here.
1. You did not get all the old oil drained out, maybe you were up on a car ramp and with the engine not level, some oil got trapped inside the engine.
2. The dipstick in not accurate. I have seen this before. Had a Ford F150 at work that showed full with 5 qts but the owners manual and the Ford dealer said 6 qts with filter. Had the wrong dipstick in there, weather done at the factory or when some jokers servicing it put in one from a car which is same but shows full in 5 qts.
3. Like was said, you are not checking it properly.
If they are overfilling the bottles, they are losing money and you can be darn sure thats one thing they must watch like a hawk. If th bottles were overfull, you would have seen oil gushing out when you grabbed hold of the plastic to pour.