I think he is responding to the OP saying that her horse drags her around when lunging, which is bad. If I understand Christopher's post, he's saying that when the horse pulls or leans on the rope, you should have the horse change direction turning towards yourself. The horse will stop pulling because it will be anticipating that a change of direction is coming. Not the actual change itself, if that makes sense. I agree if they change directions before they are asked, they should be sent back in the original direction until asked.
One thing that I also do to get them to stop pulling is bump/jerk the rope as they go around. If they pull, their nose gets bumped. Then I let them have their nose back unless they pull again. It's more of an annoyance to them to pull. But I usually do the change of directions, which will work most of the time. It's always good to have a spare technique, if what you do doesn't work.
Congrats MM! Glad to hear she's coming around.