After watching one of the videos of the guy playing the game, I think what's creepy about the it is what you as the user anticipate. Combined with some of the atmospheric effects and the weird sounds, I think user/player expectation fills in the blanks of the game, making this creepier and invoking a sense of dread. Sometimes there's nothing worse than the unknown, and nothing is more unknown than a dark hallway with, like you said, no way out. There's no aim here, no directions, no end in sight. The light flickers and the rest of the senses are muted or dulled, so the player can't rely on those to figure out what's happening. What's in the dark? More nothing? Satan? Ghosts? Someone waiting to stab you? Unicorns? Gore? Who knows.

Maybe this is creepier to those of us who have overactive imaginations. Personally, I am easily surprised when games or movies use the jump-scare tactics, but I also find those more along the lines of 'cheap thrills.'

Just out of curiosity, what in a game makes it a good horror game, or truly frightening?