you're currently going to your bsf's house with your friends because she invited you all

While driving, suddenly your car breaks down in a quiet road area. You tell your friends to get out of the car while you check the cause of your car breaking down

"It's not good for someone to be alone on the side of the road in winter like this.." Said the voice behind you, you were sure there are no other cars passing by for someone to suddenly appear..

and what does he mean by alone ..?