Such a sad case. I wonder if he possibly even fell asleep at the wheel which caused the crash. It was late at night, he's a college student who may have been studying for finals a lot lately or hanging with friends late at night and may have been tired. I remember in college losing a friend from HS who fell asleep at the wheel during daylight hours driving home for summer break and they drove off a major highway, flipping their car because they fell asleep.
Others have mentioned an animal darting out, which is possible too. I think in the case, he must have missed the animal or typically there is some sort of evidence of the animal if it's hit, such as some blood on the front of the car, damage, or even the dead animal itself. I know this unfortunately due to hitting a deer (or it hitting me) twice living in the Midwest lol.
Of course, the biggest mystery is where he went after. I can see especially if you fell asleep, you would be very disoriented when waking up. Maybe he panicked and just started walking. I imagine he is somewhere nearby but just not found yet, sadly.
I am not feeling foul play with this but won't rule anything out yet. However, it sounds like they established it was a one-car wreck with no evidence he was forced off the road. I think it would be highly unlikely someone else would just happen upon him there who decided to do him harm. Not impossible, but not probable based on what others have said here who live in the area. It sounds like all his belongings were found in the car, so no robbery happened.
The ONLY thing that would maybe make sense in terms of some sort of foul play was if he ended up making it back to the main road. It sounds like his car was found 10 miles from the main road/town area? That is a long walk - doable for most people, but he also had just been in a bad wreck. It would probably take maybe 5 hours to walk that if you were going slowly (2 miles per hour). Less than that if moving quickly. But if the firefighter called this in around, what, midnight? And his parents were notified at 2 AM which means emergency vehicles would have been on the scene by then, I can't imagine him not seeing any of them come down that road, and why wouldn't you come out and wave your arms around for help at that point?