Honestly, it could be at least partially that you don't understand relativity as well as you think you do. In many ways even special relativity is far more comp

Honestly, it could be at least partially that you don't understand relativity as well as you think you do. In many ways even special relativity is far more complex and at times counter-intuitive than is generally understood by people who have had a popular introduction to the subject and know the Lorentz transformations. That's to say nothing of general relativity which falls prey to oversimplified and disappointing analogy unless you are following the maths. Quantum mechanics is not very amenable to learning by analogy. Especially in an example like this where you're following the evolution of a state vector back and forth and the trick is in how that state is manipulated. In some ways that's a plus. You can't oversimplify important details away. I personally thought this was one of the best pieces for teaching a QC subject that I've ever read. It's clear, it flows, and it's as simple as possible and no simpler.