Girls, Is it odd for an ex to still wish you a happy birthday?

I have an ex that I don't talk to on a regular basis. To put it short, I broke up with her due to distance, and it only lasted a few months. We've been broken up for a few years. We only talk if she reaches out to me on my birthday, and she still does this even when she's in a relationship. I know I wouldn't be cool with that if my girlfriend was reaching out to an ex wishing a happy birthday, but is it me, or is that odd and just curious from a female perspective; What does that mean?

Girls, Is it odd for an ex to still wish you a happy birthday?
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