I saw the CCTV footage before it got pulled from YouTube and can say that the car involved was third in a line of traffic, and it did stop immediately and the drivers door opened before the footage ended.
If I were to speculate I would suggest the driver had assumed they were ok for the crossing as part of a group of cars and was therefore looking out towards the right hand side of the vehicle to check for oncoming traffic coming round the white building and turning opposite, as the gate started to swing in from the left.