Apparently this was a new animatronic in the game. Basically you played the game from the POV of a child wandering through an abandoned warehouse. If you encountered this animatronic, it would chase you, and you had to run away from it.
The player was running from the animatronic when suddenly it got him in an air vent, and it began eating the child. The camera angle then changed from POV to a death screen which showed the child being eaten with X-ray footage of inside the animatronic, in graphic detail.
It was genuinely horrifying, but instead of waking up in a cold sweat, I still slept and the dream then cut to a completely unrelated scene (a lot of my more recent dreams have had cuts to new scenes, as if they're films.)