Agree with the responses by newact and teacher 8....

Going forward, I suggest you extend your TN TD in the US instead of processing at the border. Same issue or nonissue may be raised at the border again. If you extend or change status with USCIS, you will have a chance to respond to Request for Evidence if any issue arises. 
Also, suggest to file CBP FOIA (Freedom of Information Act) to see what really happened at the border processing.