It wasn't just a single rifle shot but there was something semi-automatic after. If the twins could avoid any other drones they'd probably be fine provided they don't get lost somewhere because of ruins or differences between their own world and this one.

Jack on the other hand found that it was good the boys had been sent away because he rode right into the people from the Ministry around one of the corners and needed to bolt in the other direction. This was going to be worse than he thought.