Everybody has forgotten chocks including me.
Its how you deal with an error or an oversight.
If anything this clearly shows that an accident is a chain of events and some accidents are years in the making (complacencies).
This was a rented airplane, they may have been delayed into a flight after sunset, renter may have been legal for night flight with passengers but not comfortable and so on.
Could have been many additional stress factors including the attitude/behavior of a passenger.