Her text said I made her uncomfortable and that she's engaged?

I broke it off with someone years ago, and though I know it was the right thing to do, I'll always have feelings for her. This past yr I had cancer, and she contacted me on a regular basis to check up on me. I spent a month this past summer working in the city where we both lived while dating. It turned out to be very cathartic for me, given what I had gone through. Every yr for her birthday I send her a text and wish her a happy birthday. Two months ago I did that, as usual. She responded positively, wishing me the best. I told her where I was, and she responded positively as well. I added that I had decided to check out her old home, as it was nice to stroll down memory lane. After that, neither of us texted one another for two months. Last week I informed her that I would be in her town. Two days later she texted me, saying that my texts made her uncomfortable and that she is engaged. I told her that I could not understand what made her uncomfortable, but that she did not owe me an explanation; I apologized to her for making her feel that way. I also congratulated her and said I would never initiate contact again. I know I did nothing wrong, and that I gave the only reasonable response I could give. That said, I cannot imagine what I did to make her feel uncomfortable, and as someone who hates the thought of being a creep, I am still feeling a bit conflicted. Can anyone guess what my offense was?
Her text said I made her uncomfortable and that she's engaged?
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