I was recently involved in a situation where I was driving at normal speed on the highway. As I was driving, I saw a deer running across the highway. I swerved to avoid the deer, however as I was swerving the car directly behind me braked and lost control of his car, and ended up in the ditch. There were no damage to my car, as I avoided the deer and the car behind me. I pulled over to see if the man was alright, and the police came and everything, and let me go after gathering my information. My question is, who is at fault?