Accidents happen. People who are mentally “slow” are always at risk of doing something that could end very badly, but not having the mental capacity to even understand this. It’s why the family (or caretaker) is careful to ensure this sort of thing happens.
But, again, accidents happen. Apparently this one is rare in that it has only happened once.
Do you think they would have pulled the trigger that quickly if t was a muslim with a real gun?
This was no “accident”.