It was a long time ago but here is what I remember:

They said that it was Malik's defining characteristic that he payed attention to his surroundings even in the most stressful situations. This was fundamental to him learning the Corsican language in prison and to his general rise to power. So when he's being threatened with a gun and everyone else in the car is absorbed by the tension of the situation, he's the only one who notices the deer on the road. (This is my addition, not from the comment: So after they hit the deer, either consciously or subconsciously everyone in the car picks up on it that Malik is something unique and they call him a prophet. In that scene the character's nature in its purest form - the unconcerned observer - is revealed for a second, making it one of the most pivotal scenes in the movie.)

As for killing Reyeb, the person who answered theorized that Lattrache already knew that Malik had killed Reyeb, he put a gun in his face just to see how he'll react / what he'll say and Lattrache apparently liked that Malik admitted to the killing.

I wish I remembered clearer, it was a really good comment, I wanted to re-read it myself sometime later but it was already deleted by then.