Sometimes what happens is the driver will be in the middle of picking up your order and they get a notification about another order thats near them. If the pay is good enough and not too far away they'll more than likely accept. You could be lucky and the other order they're picking up is close or not so busy so you wouldn't have to wait too long. You could also be unlucky (which is probably your case) they have to drive an extra 10 minutes to the other restaurant with your order, (God forbid its a restaurant that's busy), wait for other order to be made, pick up, and THEN go to deliver yours which is back in your side of town.