I am in sales and a customer asked why I was taking a few days off. I told her, benignly, that I was having a procedure so that I can't have more kids. She immediately told me it was too personal and I apologied. A few days later, her supervisor approached me and told me she had told him and he wanted me to be aware and to not let it happen again but that he wouldn't go to my Manager. Should I let my company's HR Manager know? Or should I trust that neither the woman nor her supervisor will complain to my boss? What sort of repercussions would I expect from the HR Manager? I felt terrible, and certainly never meant to make her uncomfortable.

You said nothing wrong, and they were actually out of line.
This customer must have been a much older lady, since merely a procedure to not have any more kids is not any bad wording

I would have told supervisor nothing wrong was said, so there was noting to go to manager about.

But should I talk to my HR person? Just to be proactive so the company can protect itself? I don't want to get in trouble myself or get anyone else in trouble.. .