The family said they were following them, remember when the man and boy were in the underground shelter, they heard a dog.
The man was so paranoid about people following them that I think the family was afraid to show themselves, until the man passed.
And being it was a family the boy needed, I think it did have a happy ending, although a grim one at that.
Im not used to seeing movies with such twists, but I liked it.
Wouldnt it be terrible if that really came to pass?