You are looking at the wrong side of the crossing. Your photo is the East side, the bus is traveling West. On the West side there is quite a large cycle priority area at the stop line. The outside lane is marked as ahead and right turn. The near side lane is marked ahead only and "dock gates". The outside lane is the correct lane for the bus to be in. If somebody is in the outside lane without indicating right and stops at the traffic light suddenly to turn right, if he can't change lanes to the left he has no alternative but to foul the crossing. I think the Police would take the view that when the bus entered the box he was entitled to do so as his exit is clear.
This cab ride
shows how the crossing works at around 14.30 albeit in the opposite direction. The train is bought to a halt at a red signal. The crossing light sequence is started and the train gets an auxiliary aspect to proceed ie authority to proceed as far as the line is clear. Obviously the cab ride is on a Sunday morning the bus was probably in the morning rush but I doubt was in any danger.