welll that is what we will have to think given Maan did get injured so badly..... but Maan could have hugged geet without opening his seatbelt.... just look the way he is teaching her to drive.... seatbelt was loose enough for him to be able to put his arm around her or pull her towards him.....Well because I love geet so much and I am going to try making sense out of this situation as well. Okay so here it goes:
Well when I used to live in India I remember that we didnt have seatbelts at the back and only had them in the front of the car and since this car was hired and probably wasnt one of maan's poshce cars it didn't have airbags and second we saw maan hugging geet at the end so he probably opened his seatbelt to do so and hence he flied out of the car whereas geet remained safe.
Sorry that's all my imagination can think of to make sense out of this situation.