If you want to complete the mission as fast as possible, you can shoot the trafficker or throw a grenade and run away from the attack place. However, a better idea is to knock out the trafficker and the five soldiers, which will allow you to complete an optional objective. Hide in the grass and start shooting at them with non-lethal ammunition. Try to aim at the heads and don't let the enemies see you. When you're done, just Fulton all the opponents to Mother Base.
When you're detected, the trafficker will most probably start escaping. If this happens, you should focus on catching his as quickly as you can (get on your horse if he ran too far already). Remember that you will complete another optional objective if you neutralize the trafficker before he gets Kiziba Camp.
Note - if the trafficker managed to reach his destination despite you chasing him, sneak up to the camp to knock him out and extract him. You can also kill him with a shot from distance.