I agree that his parents are being a little over sensitive about something that was a bit out of your control.
But I'm going to have to disagree with most you guys on the response. His parents have a right to know what's going on in his life. While I believe they over-reacted, they still have the responsibility as a parent to "protect" their child. They obviously love you enough to care about what is going on in your life and don't want you harmed physically or emotionally by some "random stalker girl". Also, don't just date her for love, you'll be left a lot more hurt in the long run than the amount of pleasure you'll feel at that moment.