One of the things that must be demonstrated in a negligence case is reasonable foreseeability of the harm caused by the act or omission.
Was it reasonably foreseeable to the person who put the flyer under the windscreen wiper that it could fly off, obstruct a third party's vision and cause an accident? Probably not.
Ditto for you as the driver in ignorance of the flyer being there. If you had known and left it there there may be an argument for reasonable foreseeability.
Similarly, the driver who crashed was not negligent.
At common law (road laws may override this) each party would be responsible for the damage to their own and only their own property.
While it is true that putting the flyer on the car started a chain of events that resulted in the accident in a physical sense, it did not in a legal sense.