Daru seems stuck in a no man's land between his French roots and a reluctance to condemn the indigenous Arabs of Algeria. He refuses to follow Balducci's orders to hand the Arab over to French authorities in Tinguit.
Daru is there to teach the local people French history and culture (hence the French rivers on the chalkboard). Daru is French but was born in Algeria. He has a unique but complicated position of feeling allegiance to France and to the land that he knows: Algiers. As a result, he feels alone. Note that this is the final word in the story. He can not commit fully to either side, making it appear that he is somewhat indifferent to both sides. Daru "offends" Balducci by refusing to abide by strict French allegiance. Daru is quite hospitable to his Arab guest but when he gives him the choice of freedom or prison, he (Daru) ends that hospitality by refusing to listen to anything the Arab has to say. (Presumably, the Arab wanted to warn him that his "brothers" might seek vengeance.) So, Daru is completely torn between his allegiance to the French cause and doing the honorably thing with the Arab. In the end, he does not fully commit to either.
Balducci is less complicated. He follows the rules and is determined to stifle any uprising against the French occupation in Algeria. However, Balducci is not completely single-minded. He believes in the French cause but does show understanding. He does recognize Daru's conflicted position and let's him make his own decision regarding the Arab. As he is about to leave, Balducci tells Daru:
Don't be mean with me. I know you'll tell the truth. You're from here abouts and you are a man.
And here is where Balducci and Daru are similar. Seeing the issue is complicated, each man gives another man a choice (call it complicated free will). Balducci finally lets Daru decide what to do with the Arab. Daru inevitably decides to let the Arab choose. And lastly, the Arab shows his own complicated motivations when he inexplicably opts for the road to prison rather than seeking asylum with the nomads.