You must give way to a vehicle approaching from the right only at intersections of equal roads. Here your road with a solid surface is the main one with respect to the unsurfaced road, so you do not have to give way to the truck.
You are driving on a road with a solid surface, while the truck is approaching from an unsurfaced dirt road. Under the Rules, a road with a solid surface is always considered the main road with respect to an unsurfaced one (clause 3). Since you are on the main road, you have the advantage over vehicles entering from a secondary road, and you do not have to give way to the truck (clause 96).
Option 1. The rule of giving way to the vehicle on the right applies only at intersections of equal roads, whereas your road with a solid surface is the main one.