The RAF were good at their job. But they are only human.
The USAF bombed its own troops in WW2. In Normandy they dropped bombs short and killed the most senior American commander to be killed in NW Europe (Lesley McNair) and almost wiped out an entire division.
S*it happens.
Technically untrue, since they hadn't formed yet, but point taken. In today's world of precision directed bombing within 10 feet of a target, it is hard to remember when being within the grid square was doing well.