Rest assured that you're not the only U.S. citizens who have been subject to questioning at the border. My daughter and I travel with different surnames, a point I've been asked about at Dublin/Shannon airports on more than one occasion. (Memo to CBP: It's okay for a woman to continue to use her maiden name after marriage!)
The very best of luck with your future travels. Let us know if you have a problem the next time. Here's betting that all will be well.