If i may believe the video in my opening post, there were 1000 to 1500 casualties and 3 to 5000 combatants estimated. That can't be a robbery of a caravan or convoy anymore in my opinion. The battle took place around a bridge across a river that was in use and maintained already since 500 years before the battle and some combatants came from far so it must have been very important. Maybe some tribe(s) denied access to others and trade suffered. If the estimation would be low, like 3000 people battling, then at least 1500 people per side would have been organised. That's quite a number in those times.