@uwufujoshi
we can see that when he is running trying to reach "sangwoo" he ends up in the middle of a street and the lights turn from green to red, as we don't see any other scene after that it's kind of a resemblance he died from a car accident. Some fans also theorize that the police officer Seungbae might have been the car who killed him as he appears before the light turns red and he looks desesparate.
Hope this clears thing a bit
