Your buyer commented that they had a poor experience, there’s nothing wrong with that. There’s nothing in his/her message that violates TOS.
They ordered, you delivered and got paid.
As long as the feedback itself doesn’t violate TOS it doesn’t matter what the reasoning is. You’re free to leave your comment to that review. An exception would be if buyer tried to use a negative review to force you to give a refund. (CS would need to investigate that and they make the decision since they can see what actually went down)
I’ve hired multiple sellers myself and there’s nothing wrong with it as long as sellers get paid and fair feedback is given. I often hire 2-3 logo designers to get more options to choose from, but all designers get paid and a fair feedback.