Why does Hugh Glass look at the camera at the ending scene?

There are some brilliant ideas about what the final shot means.

Without a confirmation from the director, which I've looked for and not found yet, I personally felt the following was a great analysis, by Jeff Saporito: (my emphasis)

...The fact that Glass turns and stares into the camera is also an interesting directorial decision. Some interpretations around the Internet refer to this moment as breaking the fourth wall, but that’s not what we’re seeing. Breaking the fourth wall involves a character acknowledging the presence of the audience, drawing attention to the reaity that they are players in a cinematic environment. Glass does no such thing — his look does not imply awareness that we are watching in a movie theater. Instead, it is a thematic representation of presence. That presence he senses is perhaps something greater — life itself or a higher being. In this shot, the audience looks into the soul of Hugh Glass; Hugh Glass does not look at us.

From In “The Revenant,” what is the significance of the final shot?

Not positive, but I have to wonder if it's a reference to one of the earliest motion pictures ever made, the 1903 movie The Great Train Robbery? In the final scene one of the robbers turns to the camera and fires his pistol directly at the audience.

The scene is not directly related to anything in the main narrative, and is described as "Realism" by the accompanying letter from Edison Manufacturing.[7] Although it is usually placed at the end, Porter stated that the scene could also appear at the beginning of the film.