Technically, there was contact, so someone broke a rule. A piece of equipment, even when not in normal position, is always part of a boat.
The sticky part is the question of where the boats were (to determine overlap). If your hull or equipment (in normal position) did not overlap his hull or equipment (in normal position), then you were clear astern and were not the ROW boat. See the RRS definitions.
The next place to go is, you hit part of the other boat when you were clear astern. Technically, you broke a rule, and were not right-of-way. However, since it might be argued that this was no fault of your own (he was dragging the line), you would not be penalized.
Having said that, I personally can't see myself ever going to the room over it, or even calling for a circle. Unless it actually affected my sailing ability (stuck rudder, etc.)...
Working through the logic above, you can see that if the line hits the mark, that is definitely a foul.
BTW, I don't know if I'm an "expert." I'm just a PRO and not a judge, but this makes sense to me...
Mike