Accident: First no, then yes !?

Hello, I recently slipped a bit while parking and got to the car with a young lady. She was standing nearby and we were looking directly for a possible damage, I didn’t have one and she didn’t. I apologized for it and the thing was done for me. However, since this happened in front of my house I had offered to report to her beforehand if she needed anything. Well, four days after this incident I had a note in the letter box I’m really wondering how to notice a damage that wasn’t obvious after another four days. A witness had both me and her. Can someone give me a tip on how to keep going here? Greetings, Alex