While it is questionable that this letter is on target; why not included it? You did everything right, and you can prove it. I would include it. Since it is questionable, your examiner may second guess you and they already have a list of the complaints that you have received. At worst, they would tell you that you did not need this letter in your file. Overdisclosure is good.
Perhaps my decision would be different if you have a significant number of complaint letters. We usually have 1-2 and neither of them are CRA related, but the examiners knew that we had them before they asked for the file.
_________________________
NOLA is my Beach!