What is a "flyer"?
A flyer is the nickname for a one minute scoring mistake that just happens to be in your favor. Whatever the cause of the variety of possible scoring mistakes, the end result is that they are usually not off by three seconds or eight seconds or forty two seconds, but rather even minutes.
These scores usually stick out like a sore thumb when someone who has been mid-pack all day suddenly gets a stage win. You add a minute to their time and see that the new time would put them back in the "right" spot in the scores, and that's when you say "Looks like Johnny got a flyer on stage six, because there's no way he was that fast".