When John and Mark are sitting on the bench, John asks for the cider and when he drinks it the bottle top is off. As soon as he gives it back to Mark the bottle top appears to be back on, but he was never shown putting it back on.
The movie is supposed to take place in 2003. Two 2008 or newer cars - a Ford Fiesta and a BMW 7 series - drive past Mark as he watches John's dad drive him to school.