The article isn't about dead reckoning. The "prediction" here is the client predicting its own movement based on its (stale) state of the world and its inputs; no dead reckoning here. For other entities, you get authoritative updates from the server at low frequencies, so you interpolate to get smooth movement, and you see them "in the past" in some sense; no dead reckoning here either.

I've wrote about all this in extensive detail, including a live demo, here: https://gabrielgambetta.com/client-server-game-architecture.... (it is in fact the third "further reading" in the article).