That reminds me of the time I passed by my friend at school in the hallway, and said, "What's up?" she looked hurt and didn't respond. Later, I asked her why. She thought I said 'Shut up'. Communication Fail.
What I really want to know is why you greeted her with "Hey sweetheart" on the1st date. That's more of a 5th-10th date thing. On the 1st-5th dates you greet each other by name. The 10th date and up you start making those really horrible nicknames that make your friends sick each time you use them.