A major issue for motorbike riders is that all large, four (or more) wheeled vehicle drivers are 'out to kill them'.
I ride a motorbike every day, but I know that no one will give way to that bike.
Vans, trucks, lorries, buses ALL expect bikes to give way.
Even if the bike has the legal right of way - it is expected to give way to the bigger beasties.
I am not saying that this is what happened here but it is a major cause of death on Thailand's roads.