why didn’t the uncle look for him that night?

prolly cuz he was out on a trip or something and is coming back the next day

I think he's the one on the ambulance he seems very tired and sleepy so maybe he had an accident at work

I remember he mentioned that something happened with his hand, like where he has the scar now?

the guy in the ambulance was actually taewon's uncle. the foreman literally said, "keep taewon awake" while jun were trapped in storage room.