Actually the only torque devience from using an extension between the socket and wrench head is caused by looseness in the extension connections causing the wrench to lean over and get off center over the fastener then you would get an erroneous reading because of the leverage factor.
Now something like a crows foot extension will need to be compensated for. Extended away from the face adds torque, extending toward the handle decreases torque. If it's 90* from the inline of the wrench handle then torque is the same.
Usually that's a problem if there is a mismatch between the two. Like if the heads were shaved or milled and the bottom mating surfaces of intake wasn't matched, or the other way around. Common problem when a car overheats and warps the heads. Heads get shaved but intake doesn't, causing other problems.
You also have to remember these quick lube places are normally dealing with peoples cars that are hot. They drive them around all day then go get their oil changed.
But in all seriousness... if it was overfilled they likely didnt drain both sections of the oil pan. Common mistake.