This is all my interpretation of what Osiris saw in the infinite forest. [spoiler]Osiris saw Rasputin shoot down the Traveler during the collapse and is questioning his motive for doing so. I have long believed that Rasputin shot down the Traveler to prevent it from leaving in order to save humanity. I also believe that the big twist of this series is that the Traveler and the Darkness are essentially a process. The Traveler seeds worlds with light for the Darkness to consume. Thus, the Traveler sent out ghosts to create guardians to protect it while it healed itself. This is why guardians have had a suspicious relationship with Rasputin. The Speaker, as the voice of the Traveler, likely (and perhaps inadvertently) conveyed this message on the Traveler's behalf. So, in short, Osiris believes Rasputin is working with the Darkness. But Rasputin was doing exactly what it was programmed to do: protect humanity at all costs.[/spoiler]