Accidents happen. We almost had an accident with the Red Arrows when gliding at the Long Mynd in Shropshire about four years ago. A Glider had just been launched on the winch and two of the Red Arrows went past very low either side of the Glider that was still on the wire. They each must have missed the wire by around 100ft.
The CFI went absolutely nuts, but if they can make mistakes, anyone can.