Indeed. The sound starts off with a dialtone slowed down 700x but pitch adjusted. Guess what, that's exactly equivalent to the real dialone. (Instead of recording it for 1 second, you record it for 700 seconds.)

This rest of the video continues in the same manner. It just doesn't make any sense to me.

The point is less what it is than how one feels when it's heard. Sounds and music are often perceived passively and subtly influence your feelings at the moment, particularly the sort of "creepy music" the linked sound resembles most closely.

If you are only analyzing the component noises there's a good chance you'll miss the emotions evoked, similar to the way a joke isn't funny if you dwell too much on the explanation.