Saying "happy birthday" to someone does not necessarily mean that the person is interested in you romantically. It is a common and polite gesture to wish someone a happy birthday on their special day, regardless of the nature of your relationship. People often extend birthday wishes to friends, family members, colleagues, and acquaintances out of kindness and to acknowledge their special day.
While it is possible that someone might express interest in you through other actions or behaviors, solely saying "happy birthday" is not a definitive sign of romantic interest. If you're curious about someone's feelings towards you, it's essential to pay attention to their overall behavior, communication, and body language for more accurate clues. Building a deeper connection and open communication can help clarify each other's intentions and feelings.