A work change proposal request is used when the owner is considering making a change, and is asking how this potential change would affect the contract sum and/or contract time. They are requesting a proposal for making the change, but not approving it or allowing the contractor to proceed with it. Once the proposal has been reviewed by the owner and they would like to move forward, a change order is the document used to make this change an official part of the contract documents. See AIA G701 and AIA G709 to help you understand the difference.
I can definitely see why you chose the answer you did. As the architect, you would reject the work because the subcontractor went ahead with it without submitting proper documentation, and the owner was not consulted. The documentation should have been submitted before they did the work. I do think that the answer you chose could be an option, if the painter is able to prove that it did in fact comply with the specifications. However, this discussion should have happened before the painter proceeded. I hope that helps!